We Provide
Application Modernization Services
Modernize the platform your business depends on in planned stages, with Reenbit testing every release before it reaches your users.
Reenbit provides legacy application modernization services that bring up to 12× lower expenses to companies whose core software has become expensive to maintain and slow to change.
After a technical assessment, we move the platform to a modern cloud architecture in phases, so your data and integrations stay intact throughout the transition. Where the work is repetitive, our engineers run supervised AI agents and review every change before merging it.
Book a modernization assessment
When a Legacy Application Starts Holding the Business Back
Pega and Savanta surveyed 500+ IT decision-makers in North America, the UK, France, Germany, and Australia for an October 2025 report. Among them, 78% agreed that “the time, money, and effort spent maintaining legacy applications could be spent more productively.”
An aging application is often the hidden reason behind slow product launches and rising IT bills, long before anyone calls it a software problem. If your team recognizes two or more of the following signs, the software itself is probably what holds the business back.
Maintenance Costs Keep Growing
A growing share of your IT budget goes into patches and paid extended support for a platform the vendor no longer develops. That leaves less money and engineering time for the features your customers and sales team keep requesting.
Small Changes Take Months
Tightly coupled code means a new pricing rule or report touches dozens of files and can break something unrelated. Releases slow down as each one needs weeks of manual testing, and teams eventually stop asking for improvements.
Critical Knowledge Sits With a Few People
The original developers have moved on, and many business rules exist only in undocumented code. Each time a senior engineer leaves, fewer people understand how core processes such as billing or scheduling behave.
Integrations and AI Projects Stall
Without modern APIs, connecting a payment provider or an AI assistant means fragile point-to-point scripts and manual exports. Valuable operational data stays locked inside the old database, out of reach for reporting and automation.
Application Modernization Services We Deliver
Assessment and Modernization Roadmap
Our architects spend one to two weeks reviewing your codebase and the systems connected to it. You receive a dependency map, a risk register, a recommended approach for each component, and a phased plan with estimates. When modernization is part of a wider business change, the roadmap connects to our digital transformation consulting.
Re-architecture and Refactoring
Tangled modules and slow database queries turn every release into a risk for the operations that depend on the platform. We restructure the code around clear service boundaries and rewrite inefficient data access while existing features keep working. For a German energy technology company, we redesigned about 25 slow .NET API endpoints, cutting operations from 30–40 seconds to 3–6 seconds.
.NET Application Modernization
Many business platforms still run on .NET Framework, Web Forms, or WinForms, which no longer receive new features from Microsoft. We move them to current .NET releases step by step, replacing unsupported libraries and adding automated regression tests, so established business behavior stays the same.
Desktop to Web and Mobile Migration
Desktop software makes remote access difficult and slows down every update you ship to customers. We rebuild the product as web and mobile applications that keep the proven business logic. Reenbit moved a UK delivery software provider’s courier platform to web and mobile in a year, cutting server maintenance from $6,000 to $500 a month.
Cloud Migration to Microsoft Azure
On-premises servers tie your team to hardware cycles and manual deployments. Our engineers move applications to Microsoft Azure with automated CI/CD pipelines, changing each component only as much as the move requires. We moved a US case-management platform for public healthcare providers to Azure in phases, cutting the vendor’s expenses by up to 12 times.
Data Migration and History Preservation
Years of transactions and customer records have to survive the switch to a new system. We clean and reconcile legacy data before cutover and rehearse the migration on copies of production. For Danish wholesaler Brands of Scandinavia, Reenbit preserved 100% of Microsoft Navision history in a new SQL Server warehouse, ready for the move to Business Central.
API and Integration Modernization
Point-to-point connections between old and new systems tend to break whenever one of them changes. Our team wraps legacy functions in documented APIs and keeps partial integration with the old platform during the transition. We kept payment flows running throughout the migration for an e-commerce retailer selling across North and South America, which now covers local payment methods in 15+ countries.
UI and UX Modernization for Web and Mobile
Outdated interfaces slow down employees and make customers more likely to switch to competitors. Our UI/UX designers rework key user journeys for web and mobile, keeping familiar workflows where people rely on them and simplifying screens that waste time. Updated front ends ship in the same phased releases as the back end.
How We Use AI Agents in Modernization
Reenbit’s engineers apply AI-assisted software development to the repetitive part of modernization, with AI agents documenting old code, analyzing architecture, refactoring repeated patterns, and writing tests. A senior engineer stays in charge of every change, so the work moves faster while each line still passes the same review as hand-written code.
From Agent Task to Merged Code
01 Scoped Task
AI agent
An engineer sets a bounded task, and the agent implements and tests the change.
02 Local Commit
AI agent
The agent commits to a local branch only, and flags open questions instead of guessing.
03 Pull Request
Engineer
An engineer checks the diff, then pushes the branch and opens the pull request.
04 Code Review
Engineer
The change passes code review and regression tests, while people make architecture decisions.
05 Merge & Release
Engineer
Approved changes merge into the main branch and ship in the next phased release.
Guardrails We Apply
Every AI-assisted change on the project followed the same rules:
- Agents commit locally only, with no automatic pushes or pull requests.
- A senior engineer reviews every change before merging it.
- Agents document unresolved questions for the team instead of guessing.
- People own architecture, security, and final technical decisions.
- A shared library of about 40 engineering skills keeps the code consistent across services.
Value We Provided
With these guardrails in place, the workflow delivered the following results for a German energy technology company:
30×
faster modernization compared with traditional development approaches
90%+
of AI-generated code accepted during review without significant rewriting
3–6 seconds
for operations that previously required 30–40 seconds
Read the full case studyChoosing the Right Application Modernization Approach
In legacy application modernization, most platforms combine several approaches, because each module has its own condition and business value. Matching the approach to each part keeps cost and risk in proportion to what the business gains.
When it fits: rising hosting and database costs.
What changes: the runtime or database moves to managed cloud services on Azure.
Reenbit example: US healthcare platform moved to Azure, up to 12× lower expenses
When it fits: slow releases and frequent defects.
What changes: code structure improves, while existing features stay the same.
Reenbit example: German energy platform, 30× faster modernization with AI agents
When it fits: the current monolithic architecture blocks scaling or independent releases.
What changes: system splits into services with clear APIs.
Reenbit example: E-commerce headless front end and payment layer, 65% lower operational costs
When it fits: obsolete technology, valuable business logic.
What changes: the team rewrites the application on a modern, supported tech stack.
Reenbit example: UK courier desktop app rebuilt for web, servers $6,000 → $500 a month
When it fits: off-the-shelf software covers the process.
What changes: off-the-shelf software replaces the custom system after data migration.
Reenbit example: Brands of Scandinavia replaced Excel and SQL reporting, 100% Navision history kept
When it fits: rising hosting and database costs.
What changes: the runtime or database moves to managed cloud services on Azure.
Reenbit example: US healthcare platform moved to Azure, up to 12× lower expenses
When it fits: slow releases and frequent defects.
What changes: code structure improves, while existing features stay the same.
Reenbit example: German energy platform, 30× faster modernization with AI agents
When it fits: the current monolithic architecture blocks scaling or independent releases.
What changes: system splits into services with clear APIs.
Reenbit example: E-commerce headless front end and payment layer, 65% lower operational costs
When it fits: obsolete technology, valuable business logic.
What changes: the team rewrites the application on a modern, supported tech stack.
Reenbit example: UK courier desktop app rebuilt for web, servers $6,000 → $500 a month
When it fits: off-the-shelf software covers the process.
What changes: off-the-shelf software replaces the custom system after data migration.
Reenbit example: Brands of Scandinavia replaced Excel and SQL reporting, 100% Navision history kept
Our Legacy Modernization Process
Legacy application modernization works best when each step lowers risk for the next, since your business keeps running on the system the whole time.
Contact usWhy Choose Reenbit as Your Application Modernization Company
Companies choose Reenbit when the platform cannot stop during modernization, and the work needs engineers who understand both older and current Microsoft technology.
Deep Microsoft Stack Expertise
Most of our 100+ tech experts work daily with .NET, Azure, and SQL Server, and 89% of the team holds professional certifications. That depth matters when a modernization depends on knowing how an older Microsoft stack really behaves in production.
Phased Releases With Business Continuity
Every project moves in small production releases, and old and new components run in parallel where the business needs it. During an e-commerce migration we provided, payments in 15+ countries kept working while Reenbit replaced the legacy platform.
Fast Team Start
Modernization often starts when an internal team is already stretched, so speed of staffing matters. A Reenbit developer can join your project in about five days, and a dedicated modernization team usually starts within three weeks.
Certified Information Security
Reenbit holds ISO 27001:2022 certification and handles personal data under GDPR, a requirement for our clients in Germany, Denmark, and the UK. These rules apply at every stage of the project, from the first code review to the final handover.
Proven Modernization Results
Since 2018, we have delivered 75+ projects and published 33+ success stories with measurable results. After modernization, our clients cut running costs and release new features faster, and each story on our site shows the numbers behind it.
Long-Term Partnership After Cutover
Many clients keep working with us long after launch, so the engineers who modernized a platform continue to develop it. Our cooperation with German energy company eClou started in 2019 and has grown from one service to more than twenty.
What Clients Value About Reenbit
Reenbit’s work has streamlined processes, resulting in 50%–70% savings in time. Their use of agile methodologies has ensured a communicative and collaborative process. Their high level of expertise, proactivity, and availability is impressive.
They were highly pleased with the outcomes. Reenbit held weekly video calls for the project’s progress and used Slack and GitLab for seamless collaboration on documents and codes. Also, their respect for deadlines and budgets was exceptional.
Reenbit delivers quality work that pleases both internal stakeholders and end customers. Beyond that, they facilitate strong DevOps, agile, and testing processes. Timely and readily available, the team provides helpful suggestions and actionable solutions. Their enthusiasm sets them apart.
Engagement Models for Modernization We Offer
Choose the cooperation format that matches how much of the modernization work your own team plans to keep in-house.
Modernization Assessment
Companies that need a reliable plan before committing budget start with a fixed-price assessment sprint of one to two weeks. Reenbit’s architects hand over four documents your team keeps, whether or not you continue with us.
- Dependency map of modules and integrations
- Risk register ranked by priority
- Recommended approach per component
- Phased roadmap with estimates
Fixed-Scope
Project
When the scope is clear, we take full responsibility for a defined modernization phase, from target architecture to cutover. We agree on deliverables and milestones with you up front, and our project manager reports progress after every release, so budget and timeline stay visible.
- Scope and milestones agreed up front
- Progress report after every release
- One team from architecture to cutover
- Delivered phase running in production
Dedicated Modernization Team
Longer programs that cover several modules suit a dedicated team of Reenbit developers and QA engineers working only on your platform. The team usually starts in about three weeks and stays with the product after cutover, keeping the knowledge gained during modernization.
- Developers and QA working only on your platform
- Team starts in about three weeks
- Same engineers stay after cutover
- Knowledge kept inside the team
Staff
Augmentation
If your own engineers lead the modernization but lack hands-on .NET or Azure experience, you can add Reenbit specialists to the team. A developer can join your sprints in about five days and work within your existing processes and tools.
- Developer joins in about five days
- Hands-on .NET and Azure experience
- Works in your processes and tools
- Your engineers keep the lead
Success Stories
Discover more success stories
Explore our success stories with challenges, solutions and outcomes
Ready to create your own success story?
Talk to us!FAQ
What drives the cost of application modernization services?
The cost of application modernization services depends mostly on the size of the system and the approach chosen for each of its parts. The main cost drivers are:
- Size and condition of the codebase, including how much documentation exists;
- Number of integrations and data sources that must keep working during the transition;
- Mix of approaches, since rehosting a module costs far less than rebuilding it;
- Testing, security and compliance requirements;
- Team composition and project duration.
Reenbit starts with a one-to-two-week assessment sprint that ends with a phased roadmap and an estimate for each stage. This lets you approve the budget step by step and see what every phase will deliver.
How long does legacy application modernization take?
Legacy application modernization takes anywhere from 2 months for a focused component to a year or more for a full platform, depending on its size and the chosen approach. Our recent projects show the range:
- UK delivery software provider’s courier platform moved from desktop to web and mobile in about a year with a team of four;
- E-commerce retailer’s replatforming with new payment infrastructure ran for 12 months with three engineers;
- Data migration from legacy Umbraco, including migration of inconsistent legacy Umbraco data, reached its MVP in two months.
Because the work runs in phases, the first modernized components reach production long before the whole program ends, so the business sees results early.
How do we choose the right application modernization company?
When choosing an application modernization company, look for proof that its engineers have changed live systems without disrupting the business. Questions worth asking:
- Which similar platforms and technologies has the team modernized, and what were the measured results?
- How does the vendor assess your system before it quotes a price?
- How are releases tested, and what happens if a cutover goes wrong?
- Who owns the code, documentation, and system knowledge after handover?
- How does the team use AI, and who reviews its output?
Can you modernize an application without downtime for our users?
Most application modernization projects can run without noticeable downtime when the team phases the work and can roll back every release. Reenbit keeps old and new components running side by side and moves functions or user groups over gradually. Before each release, automated regression tests check the workflows people rely on, and every cutover comes with a rollback plan.
For an e-commerce retailer selling across North and South America, we kept partial integration with the legacy platform throughout the transition to avoid service disruption. Some projects still need a short maintenance window for the final data switch. In that case, our team plans it together with yours for the hours with the lowest traffic.
What is the difference between application modernization and cloud migration?
Cloud migration changes where an application runs, and application modernization changes the application itself. The difference shows up in the results:
- After a cloud migration (rehosting), the code, architecture, and most of its limitations stay the same;
- After modernization, the team updates the code, architecture, data, and interfaces, so the system becomes easier to change and cheaper to run.
The two often go together. Many projects begin by moving workloads to Azure and then refactor the parts that slow the business down. For a US case-management vendor serving public healthcare providers, Reenbit combined both approaches, rebuilding the platform in phases while moving it from on-premises servers to the cloud and cutting expenses by up to 12 times.
What do you need from our team during modernization?
Application modernization services from Reenbit need a small but steady commitment from your side, mostly from people who know how the business uses the system:
- Product owner who sets priorities and accepts each release;
- One or two domain experts for interviews during the assessment sprint and for checking business rules later;
- Access to repositories, environments and existing documentation, with someone who can grant it quickly;
- IT or DevOps contact for infrastructure, security reviews and cutover windows.
Your developers can join the work or stay focused on daily operations. The assessment sprint shows how many hours each phase needs from every role, so you can plan their time before the main work starts.
Do we have to move to Azure, or can we stay on-premises?
Application modernization does not require a cloud move, so the decision depends on your costs, compliance rules, and plans. Most Reenbit projects run on Microsoft Azure, because that is where our engineers have the deepest experience. The common options are:
- Stay on-premises and modernize the code, architecture, and interfaces first;
- Go hybrid, moving selected services such as APIs or reporting to the cloud while core data stays on your servers;
- Move the whole platform to Azure in phases, as we did for a US case-management vendor that cut expenses by up to 12 times.
Do you modernize non-.NET platforms such as Java, PHP, or Delphi?
Reenbit’s core legacy application modernization expertise is .NET and Azure, but our engineers also work daily with JavaScript stacks. We built the UK courier platform on Node.js and React, and other projects run on Angular and Vue. For Java, PHP, Delphi, or other older platforms, the assessment shows which path fits best:
- Migrate the system to .NET or a Node.js back end with a modern front end;
- Keep stable legacy modules and wrap them in documented APIs;
- Rebuild only the parts that block the business and retire the rest.
Can we keep releasing new features while the platform is being modernized?
During legacy application modernization, your product roadmap does not have to stop, because the platform changes module by module. Feature work usually runs in parallel like this:
- New features go into modules that are already modernized whenever possible, so the team builds them only once on the new stack.
- Developers make urgent changes to legacy parts in the old code and carry them into the new version during the next phase.
- Your team and ours work from one backlog and release plan, so priorities stay visible to everyone.
- Automated regression tests check existing workflows after every release.