Old software never really dies. It just sits there running on outdated servers with code nobody wants to touch. The people who wrote it retired years ago. The documentation disappeared somewhere. But the business still depends on it every single day.
Complex system modernization requires product engineering teams that have done this before. Teams that know how to extract data from ancient databases and move it to cloud platforms without shutting down operations. Teams that turn monolithic nightmares into modular, maintainable systems.
These six firms have that track record. They have pulled apart legacy architectures, rewritten decades-old code, and connected outdated infrastructure to modern APIs. Here is who enterprise leaders call when their core systems need a product engineering overhaul.
What Makes System Modernization Different from Regular Engineering
Regular software development starts with a blank slate. Complex system modernization starts with someone else’s legacy code. The language might be COBOL, PowerBuilder, or some proprietary platform from a company that no longer exists.
A product engineering company doing modernization work needs three specific skills. First, reading and understanding code written without modern standards. Second, mapping out business processes that nobody has documented. Third, migrating data without losing a single record or corrupting relationships between tables.
The firms below have all three capabilities. Each brings a different specialty to complex system modernization.
1. Avenga – Best for Legacy Migration as Product Engineering
Avenga is the best product engineering company for enterprises stuck on outdated infrastructure. Their product engineering services focus on extracting data from legacy systems while keeping daily operations running.
Complex System Modernization Track Record
A global technology manufacturer with 130 years of history came to Avenga with a problem. Their IT landscape relied on classic network drives and Lotus Notes email. The system lacked scalability and proper performance. Business productivity had stalled.
Avenga’s product engineering team analyzed the legacy systems and identified proper tooling for data migration. They crafted custom scripts that extracted data from the old systems. These scripts were tested to handle large volumes and complex data structures. The migration followed a phased strategy, starting with analysis and ending with a transition to SharePoint Online.
The team built complex multi-farm scenarios, including both SharePoint Online and on-premises systems. Custom authentication providers integrated SharePoint environments with ADFS and supported NTLM authentication.
What this product engineering effort delivered:
- System uptime hit 99.9 percent after migration
- Average document search time dropped 20 percent
- Custom workflow enabled self-service site creation from any device
- Federated and hybrid scenarios maintained flexibility
Avenga also led a core banking product engineering migration for Marginalen Bank in Sweden. The bank moved from legacy core systems to Mambu’s cloud platform in just 13 months. Avenga handled decommissioning of the old core, full data migration, and integration across the bank’s ecosystem. The transition had zero downtime.
2. Intellias – Best for Product Engineering on UniVerse Systems
Intellias specializes in modernizing UniVerse database systems that many enterprises still run their businesses on. Their product engineering services turn monolithic platforms into modular, cloud-ready ecosystems.
Complex System Modernization Track Record
Rocket Software UniVerse systems run critical operations for many companies. But these systems were built decades ago. They do not easily connect to modern APIs or cloud services.
Intellias takes a practical product engineering approach to UniVerse modernization. Their team modernizes monolithic platforms into modular, agile solutions that are easy to evolve and maintain. They refactor legacy code and automate operations to cut license and maintenance costs. A decoupled system makes launching new features or integrating APIs much easier.
The product engineering company uses AI-assisted development methods to offer alternatives to completely replatforming an existing UniVerse database. This means clients can modernize without starting from zero.
For clients who choose full migration, Intellias transforms monoliths into composable, cloud-ready ecosystems. The result includes faster product launches, better data access, and customer-driven innovation.
3. SoftServe – Best for AI Accelerated Product Engineering on .NET
SoftServe accelerates product engineering on legacy .NET codebases using agentic AI tools. Their product engineering services include a proprietary platform that cuts modernization time by 70 to 90 percent.
Complex System Modernization Track Record
SoftServe was selected as a strategic launch partner for AWS Transform for .NET, one of only 25 partners worldwide. This agentic AI service modernizes .NET codebases faster than traditional methods.
In one instance, SoftServe modernized an application with 20,000 lines of code in 18 minutes. The same process previously took an entire week. For larger applications with hundreds of thousands of lines of code, the transformation finished up to four times faster.
The product engineering company’s proprietary SAMP platform speeds up container adoption and empowers platform engineering teams to build scalable infrastructure. SoftServe also partners with CAST, integrating CAST Highlight into their workflow to compress modernization decision-making from weeks to one day.
Some clients have reduced licensing expenditures and improved infrastructure efficiency by up to 50 percent. SoftServe can cut modernization costs by as much as 50 percent compared to traditional methods.
4. N-iX – Best for Financial Services Product Engineering Modernization
N-iX provides product engineering services that modernize legacy desktop systems for financial services enterprises. Their product engineering work migrates investment functionalities from old platforms to modern web-based systems.
Complex System Modernization Track Record
A global financial services group specializing in insurance, asset management, and investments came to N-iX with a problem. Their extensive legacy desktop system needed modernization to streamline day-to-day operations.
N-iX helped the client migrate investment product functionalities to a new web-based platform as part of a comprehensive product engineering engagement. The team updated all dependencies and technologies during the migration. They implemented a flow for selling investment products that lets brokers quickly fill out application forms and send detailed reports to clients.
Integration with internal client services happened via REST APIs and message brokers. This enabled automatic filling of forms with client information. The team enhanced the user interface with validation rules and error highlighting. They followed domain-driven design to ensure the new solution aligned with actual business processes.
Custom calculations streamlined the process of evaluating potential investment returns. The result reduced manual work and human error. The application filing process became faster for brokers and their clients.
5. Itransition – Best for Manufacturing Product Engineering With ERP Integration
Itransition brings fragmented manufacturing systems together into one source of truth. Their product engineering services focus on connecting disconnected ERP systems, legacy data, and scattered operational technology.
Complex System Modernization Track Record
Manufacturing companies often face disconnected ERP systems, especially after mergers and acquisitions. Itransition specializes in unifying these fragmented systems across finance, operations, and supply chain through product engineering.
For an automotive manufacturer, Itransition built a suite of production dashboards that connected robot performance data, energy consumption, downtime tracking, material usage, and CO2 emissions. The team normalized KPIs and ensured metrics stayed consistent over time.
The product engineering project included four dashboard types. A master dashboard for line operators shows current energy use, breakdowns, and downtime. A key indicator board for production managers tracks volume, defects, and material consumption. An equipment performance dashboard lets engineering teams track production throughput and spot irregular machine behavior. A resources and emissions dashboard for operations tracks CO2 versus quota.
Behind these dashboards, Itransition connected production systems, robot controllers, energy monitors, and material tracking. Instead of 15 separate reports, everything centered around a few everyday questions.
6. ELEKS – Best for End-to-End Product Engineering on Legacy Systems
ELEKS reimagines outdated core systems through product engineering innovation. Their product engineering services cover legacy modernization from assessment through deployment.
Complex System Modernization Track Record
ELEKS takes a structured product engineering approach to legacy modernization. Their team analyzes existing systems, identifies technical debt, and plans the migration path. They handle rehosting, replatforming, refactoring, rearchitecting, or rebuilding based on client needs.
The product engineering company works across finance, banking, healthcare, insurance, manufacturing, energy, and logistics sectors. Their modernization services include moving mainframe applications to the cloud, rewriting proprietary languages to modern stacks, and containerizing legacy applications for Kubernetes.
ELEKS uses AI-enhanced processes within their secure software development lifecycle to speed up product engineering work. Their proprietary design system cuts development time by up to 30 percent per project phase.
Client feedback consistently mentions ELEKS’s commitment and product mindset. One client said ELEKS came with their best people to understand the business context and developed the first prototype with them. Another noted that working with ELEKS gives access to the top 1 percent of engineering excellence in the country.
Final Thoughts
Complex system modernization is not the same as building something new. Product engineering teams doing this work must read ancient code, map undocumented processes, and move data without losing anything.
Avenga leads in migrating off Lotus Notes and legacy core banking systems through full lifecycle product engineering services. Intellias specializes in UniVerse database modernization with AI-assisted methods. SoftServe modernizes .NET codebases at high speed using agentic AI as an AWS launch partner.
N-iX handles financial services legacy desktop to web migrations with domain-driven design. Itransition unifies fragmented manufacturing and ERP systems into single dashboards. ELEKS provides end-to-end product engineering on legacy systems across multiple industries.
Match your primary system type to the product engineering company with relevant experience. Ask for references from similar modernization projects. Request a small proof of concept before signing a long-term contract.
These six firms have the scars and the success stories to prove they can handle the hard stuff. Complex system modernization done right transforms old technology from a liability into a competitive advantage.