Windows desktop application specialists
We keep business-critical Windows applications fast, secure and shipping.
Number Six is a senior-only practice for WPF, WinForms and WinUI. We diagnose before we quote, modernise one slice at a time, and have no platform of our own to sell you.
Fixed-price assessments from £4,500. Remote across the UK, Europe and the US East Coast.
Start here
Most people arrive with a symptom, not a project
Pick the one that sounds like your week. Each leads to a fixed-price piece of work that ends in a written answer.
Stutter under load, creeping memory, a UI that freezes on the wrong thread. We profile it and give you a root cause per symptom, not a list of guesses.
Performance, memory and threading → “We’re about to fall out of support.”.NET 8 and .NET 9 both end support on 10 November 2026. .NET Framework 4.6.2 follows in January 2027. We move you to .NET 10 without breaking the application.
Upgrades and migration → “Installing and updating it is a nightmare.”MSI, MSIX, ClickOnce or a custom updater; code signing, silent install, staged rollout and rollback. We decide it properly and build you the pipeline.
Packaging, deployment and updates → “Windows 11 or Arm64 broke something.”New Windows releases keep changing the ground under old code. We reproduce the failure in a lab against your build and tell you exactly what to change.
Compatibility readiness → “One person understands this application.”Key-person risk is the most common reason we get called. A Health Check documents what is really in there; a support plan makes sure someone else knows it too.
Health Check → “A customer is asking for evidence.”Accessibility conformance for public-sector buyers, and the Cyber Resilience Act for anything sold into the EU. We build the technical evidence you have to show.
Accessibility and CRA readiness →The ladder
Three ways to work with us, in the order most people use them
You are never asked to commit to a large project before anyone has looked at the code.
One — Diagnose
Assessments
A fixed-price, fixed-duration investigation that ends in a written report: severity-ranked findings, the artefact that proves each one, and a prioritised plan with effort ranges.
From £3,500. Five days to five weeks.
Two — Repair and modernise
Projects
Scoped from the assessment, so the price is real. Upgrades, performance remediation, incremental UI modernisation, installer pipelines, Arm64 ports, architecture refactors.
From £8,000. Two weeks upward.
Three — Keep it alive
Support plans
A named engineer who knows your application: monthly regression checks against Windows and runtime updates, security triage, small changes, and release management.
From £1,500 a month.
Why now
Four dates that will decide your next twelve months
Desktop software rarely moves because it is old. It moves because something external forces it: a Windows rollout, a runtime leaving support, an audit, a customer’s procurement questionnaire. Those triggers are published in advance, so they can be planned for instead of survived.
- 11 Sep 2026EU Cyber Resilience Act — reporting duties begin24-hour early warning, 72-hour notification
- 10 Nov 2026.NET 8 and .NET 9 — end of support.NET 10 becomes the only supported target
- 13 Jan 2027.NET Framework 4.6.2 — end of support4.7–4.8.1 follow the Windows lifecycle
- 11 Dec 2027Cyber Resilience Act — applies in fullSBOM, vulnerability handling, CE marking
What makes us different
Everyone else in this market is selling you a destination
Tool vendors want you on their converter. Framework vendors want you on their framework. Offshore teams want a large rewrite with a lot of people on it. All of them have a commercial answer before they have seen your code.
We have nothing to sell but the engineering. Sometimes the honest recommendation is to stay exactly where you are and fix six specific things — and when the answer is to move, the destination follows your constraints, not our partner agreements.
A working application is an asset, not a liability. Most of them deserve maintenance, not a rewrite.
- Senior only. The person who scopes the work is the person who does it.
- Evidence, not opinion. Every finding ships with the profiler trace, memory snapshot or failing test that proves it.
- AI-accelerated, expert-verified. We use modern agent tooling to do the mechanical part faster, and charge for the judgement that the tools get wrong.
- Fixed price at the front door. Assessments are quoted as a price, a duration and a deliverable.
- Written-first. Reports and recorded walkthroughs, so distance and time zones stop mattering.
Start with a diagnosis, not a proposal
A Health Check is a fixed price, a fixed duration and a written report you own — whether or not you ever hire us again.