Legacy Modernization Specialists No-Downtime, Parallel Run

Modernize your legacy system. without stopping your business.

We take systems people built twenty years ago (VB6, WinForms, WCF, ageing .NET, old Java and C++) and move them onto modern platforms in phases. The old system keeps running while the new one is built, tested against your real data, and only then switched over.

Old and new together: parallel run during the move
Phased, not big-bang: you decide when we switch
Current targets: .NET 10 · Angular · React · Flutter

Our products, running in production

Hospitality back-office automation
INNRLY

Back-office software for hotels that does the night audit, reconciliations and labor reporting overnight, so the work that used to eat your mornings is already done when you walk in.

  • Night audit & OTA commission automation
  • PMS-to-accounting reconciliation: Opera, OnQ, FOSSE, HotelKey
  • Vendor invoices pulled from portals and matched automatically
  • Labor snapshots that surface overtime before it hits payroll
  • Live at 200+ hotels, saving 20–40 hours per property each month
September 2026

INNRLY joined M3's partner ecosystem as an Associate Partner. Invoices are captured and GL-coded automatically, then delivered into M3 Accounting Core for month-end close.

innrly.com →
Smart building & property management
Allistic

The control center for a smart property: access, energy, security and automation brought together in one mobile app for residents, owners and developers.

  • Smart access control with mobile entry & guest management
  • Energy management: HVAC and lighting tuned to cut power bills
  • Smart apartments: locks, thermostats and lighting in a single app
  • Security with video surveillance and real-time alerts
  • Running in real buildings, like Latitude Apartments, New Orleans
Works with the equipment already on site
Climate
ecobee Honeywell Resideo Seam
Access & locks
Yale / August Avigilon Brivo DUSAW Yalex Honeywell Resideo Seam
Lighting
TP-Link
Appliances
GE Appliances LG ThinQ
Video intercom
Chamberlain Group LiftMaster MyQ
Entry & delivery
Swiftlane Package Nexus
Tenant services
Doorloop Plaid TransUnion
allistic.co →
What we do

Three things, done properly, rather than seven things done loosely.

Legacy modernization

We migrate WinForms, WCF/WPF and older C++ and VB systems onto .NET 10, Angular, React or Flutter, without the "rip and replace" gamble. The business logic your team already trusts stays the same; only the platform underneath changes. Old and new run side by side until you're ready to cut over.

How we do it →

Custom software development

Web, mobile and backend systems built on .NET, Angular, React, Flutter, Python/Django and NestJS, matched to what your team actually needs to run the business, not whatever framework is trending this month.

Our services →

AI-driven automation

We build AI into the systems we deliver, aimed at real workflow steps (document processing, data reconciliation, reporting, support triage) so the software quietly does more of the repetitive work on its own.

How we use AI →
The short answer is yes

Can your legacy system be modernized without breaking it?

Almost always. The fear is understandable. A system that's been running the business for years feels too fragile to touch. We treat it that way. Here's how we keep it safe.

We never switch off the system that's paying the bills.

Most legacy projects fail because someone replaces a working system in one go and hopes for the best. We do the opposite: the old system stays live the whole time. We build the new system beside it, feed it the same data, and let the two run in parallel until the new one has proven itself in real use.

When we finally cut over, you choose the moment. And if anything looks off, we step back to the old system; it's still there, still running, still current.

  • Parallel run Old and new systems serve the same users at the same time, for as long as you need.
  • Dual-write New data flows to both systems in real time, so the new one is always testable against live activity.
  • Phased cutover We move one module at a time, not the whole business in a weekend.
  • A rollback path Until you're fully confident, we can redirect traffic back to the old system in minutes.

Same business rules

We port the logic you trust; we don't invent new ones. Changes are your decision, made deliberately.

Fixed scope first

A short paid assessment gives you the phase plan, timeline and budget before any code is written.

Client story

Peregrine Connect: rebuilding the core of an integration platform

An enterprise integration platform used across financial services, healthcare and retail needed its core rebuilt for scale without disrupting the systems that already depended on it. That's the down-to-earth version: the new core was built and verified in parallel, then swapped in.

Diagram of the rebuilt Peregrine Connect integration architecture

What the migration involved

We re-architected the core modules on .NET with modern patterns, built custom connectors for data exchange between systems that didn't talk to each other, and put API management and security in place for high-volume traffic.

  • PerformanceRebuilt for thousands of concurrent transactions with minimal latency
  • SecurityAPI management and access control across every connector
  • ScopeFinancial services, healthcare and retail integrations

Read the full case study

We work across time zones, not around them

Where your team already meets ours.

We build for clients across the US, UK, Europe, the Gulf, Australia, the Americas and India, and we schedule real overlap with your working day, wherever you sit.

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United States

Starts your morning, ends your night

Your team signs on, ours is already mid-sprint. Anything raised late in your afternoon gets built overnight and lands before your next standup.

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United Kingdom & Europe

5–6 hours of real overlap

Close enough to a shared working day that we can pair on a problem live. GDPR and UK GDPR alignment is default on every engagement, not an add-on.

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Gulf Region

Two hours out, same working rhythm

Close enough that a call lands when you expect it to. English is the working language end to end, and our team has shipped integrations used across the GCC.

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Australia & New Zealand

Overnight is our handover window

Your morning starts with code that already works, plus notes explaining what changed while you were asleep. No archaeology required.

🌎

North & South America

Evening queue, morning delivery

A backlog does not sit untouched overnight. When you log in, the diagnostics and results you asked for are waiting.

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India

Local hours, on-shore conditions

ERP rollouts, integrations and product teams for Indian businesses. Same engineers, same standard, no timezone maths on your side.

Straight answers

Questions people ask before they call us.

Can you modernize a legacy system without downtime?+
Yes. We build the new system alongside the old one and run both in parallel, comparing results against live data. We only switch over once the new system is proven, and we keep a rollback path until you're comfortable.
Which legacy technologies do you work with?+
VB6, WinForms, WCF and WPF, ESB and legacy messaging, older .NET Framework, ageing Java and C++ systems, and older ERP installs. If your software is still doing a job for your business, it can usually be modernized rather than replaced.
How long does a migration take?+
It depends on the size of the system. We start with a short assessment, usually one to two weeks, that produces a scope, a phase plan and a fixed budget before any line of code changes.
What happens if something goes wrong during the switch over?+
Because the old system is still running in parallel, we can point traffic back to it in minutes. The cutover is planned, tested and reversible. We never do a one-big-bang switch that can't be undone.

Got a legacy system that's overdue for a closer look?

Talk to an engineer