LondonApp & Custom Software Development in London
Software development for London. We build professional mobile apps and websites for UK businesses across all sectors.
App369 is a founder-led software studio based in Miami, Florida. Simon builds custom mobile apps, web platforms and AI features for businesses in London and beyond, working remotely on Eastern Time.
- Fiverr
- 5.0 · 127 reviews
- Own product
- Workspace369
- Fixed-price offers from
- $450
Same fixed prices wherever you are
Fixed scope, fixed price, paid upfront. The work happens in writing; no call needed.
- App Fix Ticketfrom $450One reproducible bug in an existing mobile or web app, diagnosed and fixed.
- AI-Built App Rescuefrom $450A Lovable, Bolt or Cursor app checked end to end in 3 days, then its worst problems fixed at a fixed price.
- Web App MVP Sprintfrom $6,000A scoped web app MVP in Vue/Nuxt or React, with a fixed quote after a $450 written scoping.
- Monthly Dev Subscriptionfrom $1,495/monthOne development request at a time, most back in about 2 business days. Pause or cancel anytime.
Why App369
Why London Businesses Choose App369
What London teams should know before working with App369.
Serving London, Greater London, and the entire UK
Focus on UK business regulations and GDPR compliance
Focus on fintech, e-commerce, and enterprise solutions
Understanding of the UK market and business culture
What Simon builds
Software Development Services in London
From the City to Canary Wharf, we build software that meets the high standards of London businesses.
Mobile Apps
iOS and Android apps built with Flutter from one codebase, from concept to App Store launch.
- iOS & Android
- Cross-Platform
- App Store Optimization
- Maintenance & Updates
Web Development
Fast websites and web applications, built for search and for phones first.
- Custom Design
- E-Commerce
- SaaS Applications
- SEO Optimization
Custom Software
Internal tools, integrations and back-office systems engineered around how your team already works.
- Enterprise Development
- API Integration
- Cloud Migration
- Technical Consulting
How it works
The 4-Phase Development Process
A written scope and four clear phases keep London projects predictable.
Discovery
Understanding your vision, goals, and market requirements through stakeholder interviews and competitive analysis.
Design
Creating clear UI/UX with interactive prototypes you can click through before the build starts.
Development
Building with Flutter, Vue.js, Node.js, and GCP using 2-week Agile sprints with weekly milestone reviews.
Launch
Deployment to production with crash and uptime monitoring and ongoing maintenance.
Technologies
- Flutter
- TypeScript
- Node.js
- GCP
- Firebase
- Vue
- JavaScript
- Python
Questions
Frequently Asked Questions
How long does a typical project take?
It depends on scope. As a rough guide, a marketing website takes 4-8 weeks, a web application 2-4 months, and a mobile app 3-6 months. Every London project starts with a written scope and milestone plan, so you know the timeline before any build work starts.
Do you provide ongoing support?
Yes. After launch App369 offers maintenance that covers bug fixes, iOS and Android OS updates, security patches, dependency upgrades and small feature work, so your London app keeps working as the platforms change.
What's your pricing model?
Fixed-price offers are paid in full before work starts, at the prices published on the fixed-price page. Larger builds start with a paid scoping and are then quoted in writing, with their payment schedule, and start only with your yes.
Can you work with existing projects?
Yes. Simon takes over existing codebases, especially Flutter and Firebase apps, for code audits, bug fixes, new features and migrations. London businesses with an app that stalled or a developer who left can start with an audit before committing to a larger build.
What technology do you use?
Mostly Flutter for iOS, Android and web apps from one codebase, Firebase and Google Cloud for backends, and Vue/Nuxt for websites. For AI features Simon integrates large language models for assistants, document extraction and automation.
Your Development Partner
Simon Dziak
As founder of App369, I personally oversee every project App369 takes on, from scoping to launch. I build with Flutter, Firebase and Google Cloud, and I also built and run Workspace369, a client-management platform for freelancers and small businesses. Based in Miami, Florida, I serve clients across London and nationwide.
Start Your London Project
Fiverr reviews / 95 on app work
What buyers said about working with Simon
“Extremely thorough work! Szymon went above and beyond to make sure we were happy and that the job was 100% complete. He was respectful, flexible, and a great listener. We look forward to working with him again in the future. Thank you Szymon!”
A buyer in the United States, October 2020. App development on Fiverr “SZYMON IS THE BEST DEVELOPER ON FIVERR! First of all, the customer service was amazing! He answered all my questions, and help me figure it out the best way to achieve my desired application. Additionally he also submitted my application to the App Store and Google Play! Strongly recommend! I am definitely going to be coming back!”
Mark, United States, October 2020. App development on Fiverr “Working with Simon makes everything run so smoothly and better than I could ask for it. Amazingly communicative, extremely knowledgeable of coding and the backend processes. I strongly recommend.”
A buyer in the United States, January 2026. App development on Fiverr
Read the whole story
- Sixteen five-star reviews from one buyer: mobile apps, app design and a Shopify store (Mark, United States)
- A large custom app build, delivered on the back end and the front end (A buyer in the United States)