We are a Paris-based senior team that works your hours, ships to the App Store in 3 to 5 months, and costs roughly half of a comparable US agency. Not because we are junior. Because Paris is not San Francisco.
Calendly direct. You will talk to a senior engineer within 48 hours.
A common reaction on the first call is some version of "this is suspiciously affordable for what you describe."
It is not. Here is the math.
A senior React Native engineer with 8 years of experience costs us roughly 40% of what the same profile costs a US agency in San Francisco or New York. Lower base salaries, lower social charges relative to total comp, no employer-paid healthcare, lower office costs. None of that has anything to do with skill.
US agencies bill you a senior rate but staff your project with juniors managed by one senior. We do not have juniors. Every engineer on your project has shipped at least one production app to the App Store. Fewer people, all senior, fixed scope.
We are online 9am to 4pm Eastern Time. Your daily standup, your design reviews, your urgent decisions, all happen during your business day. You do not wait 16 hours for a reply.
A greenfield iOS + Android app that a top-tier US agency would quote at $180k to $300k, we ship for $50k to $120k. Same App Store quality, same engineering rigor, same senior team. A different cost structure on our side.
Selected clients across Europe and the United States
A few of the products we have shipped to production
Visto
Mobile · Social discovery · Location-based
Mariia
Mobile · Parenting × neuroscience · AI
Métaforma
Internal SaaS · B2B operations
US auto-import platform
Web · Cross-border commerce · AI agents
Every project on this page is one we built end-to-end and that is in production today.
Our mobile app development services for the US market are built around one stack: React Native, with native modules when the app needs them. iOS and Android from a single codebase. Backends in Node or Postgres-friendly stacks. AI features (LLM integration, RAG, agent workflows) when they genuinely improve the product.
You have a product spec or a Figma file. We take it from zero to App Store, typically in 3 to 5 months.
$50k – $120k
Your current app is slow, crashing, or stuck on a stack the original team moved on from. We take ownership, stabilize, and modernize.
$40k – $90k
You want a chat assistant, document intelligence, or AI-driven UX inside an existing app. We have shipped these on production traffic, including agentic flows.
$25k – $60k
Project budgets start at $25,000. We work on fixed-scope engagements with milestone-based pricing. Typical engagement length: 3 to 5 months for a greenfield app, 6 to 10 weeks for a focused rescue or AI feature build.
Four products. Each one we built end-to-end, each one shipping in production.
Mobile · Social discovery · Location-based
Stack: React Native · Expo · Geolocation · Push
Instagram meets Happn, a photo-driven social app where the people you cross paths with become matches surfaced through their feed. We owned the full mobile build from spec to App Store, including the geolocation pipeline, native push notifications, and the moderation layer.
Live on iOS and Android · Native geolocation · Production traffic since launch
Mobile · Parenting × neuroscience · AI
Stack: React Native · OpenAI · RAG · Vector DB
An AI parental copilot blending Montessori pedagogy and neuroscience research, delivering personalized 24/7 advice through a generative engine running RAG over thousands of expert sources. We built the consumer app from scratch alongside the founder, owning iOS and Android delivery end-to-end.
iOS + Android in production · RAG over thousands of expert sources · Serving families daily
Internal SaaS · B2B operations
Stack: React · Node.js · AWS · Stripe · LLM features
An end-to-end ERP redefining how training organizations run. We delivered the critical modules; Qualiopi-compliant admin, billing automation, marketing funnel, integrated LMS; replacing 5+ disconnected SaaS tools. Mobile access for field teams and AI-assisted data entry on top.
5+ SaaS tools replaced · 3× admin-time reduction reported by users · Field-team mobile access
Web · Cross-border commerce · AI agents
Stack: TypeScript · LLM matching · Distributed scrapers
A US-based importer of classic American cars for European buyers needed to monitor every public US listing - eBay, Bring a Trailer, dealer sites, Craigslist - and surface vehicles matching each client’s mandate. We built a distributed scraping pipeline ingesting thousands of listings daily, plus an LLM layer that scores every match against the client’s criteria with explainable output.
Thousands of US listings ingested daily · LLM-scored matches · Live in production
What clients say · 4.9/5 across Sortlist and Google · 35+ reviews
“Roger and his team are exceptional professionals: competent, thoughtful, responsive, and always delivering on time and to spec. We have several major projects running with them and could not be more satisfied.”
Gadiel Ngoma
CEO, Hwell · Sortlist review
“We genuinely felt heard, understood, and supported at every step. Concrete advice, smart solutions, fast progress in the right direction with no unnecessary stress. Pretty rare in this kind of collaboration.”
Marcel Corrieri
Executive, Izippizi · Sortlist review
“Communication with Ruji is easy and fast. Highly responsive team, attentive to client feedback. On a fairly unusual project, every requested change was made so the final result matched exactly what I hoped for. Signing up for V2.”
Johann Poisson
Client · Google review
Read all reviews on Sortlist.
We are React Native specialists first. We ship AI features when they make the product measurably better, not because the deck has the word "AI" on it. Three patterns we have shipped on production traffic for paying users:
Your domain content, indexed and surfaced through chat or guided flows. Built for Mariia, a parental copilot indexing thousands of expert sources across Montessori pedagogy and neuroscience.
Stack: OpenAI · Vector DB · Python
Score candidates against criteria, with explainable output the operator can trust. Built for a US auto-import platform matching seller listings against client mandates.
Stack: TypeScript · LLM · Scraping pipelines
Pipelines that ingest unstructured input - PDFs, web pages, emails - and produce structured records. Built for B2B SaaS internal tools where data entry is the bottleneck.
Stack: TypeScript · LLM agents · OCR
Across all three: we ship the LLM layer alongside the React Native or web app, not as a bolt-on. We pick models pragmatically (OpenAI, Anthropic, open-source) based on cost, latency, and accuracy for the task, and we tell you when AI is the wrong answer.
We are React Native specialists. Here is our honest take on when it is the right call.
You need iOS and Android from day one. You ship features weekly. Your team is small, or your engineering capacity is borrowed from another product. You want a single codebase that scales as you hire. You would rather ship in 4 months than in 9.
You are building a real-time, latency-critical interaction - high-end games, AR/VR, real-time camera vision pipelines. You need deep platform-specific APIs at the heart of the product, not at the edges. Your team already has senior native engineers and the engineering culture to maintain two codebases. In those cases we will tell you so on the call, and point you to teams better suited to the work.
Most of our clients sign the full engagement after a paid 2-week Pilot Sprint. It is the lowest-risk way to work with a senior team you have just discovered.
Before committing to a $50k+ build, we run a 2-week paid sprint that delivers:
If you sign the full project, the $5,000 is credited 1:1 against the first milestone.
If you do not, you keep everything we produced and can hand it to any other team.
Book a 30-min technical call to scope a Pilot SprintFour phases. Fixed scope, named owners, milestone-based pricing.
30 to 60 minutes on call. We map your product against the React Native ecosystem: what is standard, what needs a native module, what is risky, where the schedule risk lives. You leave the call with a concrete view, regardless of whether you sign with us.
A fixed-scope proposal with a phased timeline, milestone-based pricing, and named senior owners on our side. The number you sign for is the number you pay.
You get a Slack or Discord channel with the team, a weekly demo of working code, and a shared backlog you can re-prioritize at any time. Releases ship to TestFlight from week 3.
We submit to the App Store and Play Store, run the launch, and stay engaged for 60 days post-launch to fix anything we shipped. After that, you can either keep us on retainer or take ownership of a clean codebase.
Five commitments, written into every engagement.
Scope changes go through a written change request before any work starts; no surprise invoices, ever.
You own everything from the first commit. IP transfers on each milestone payment, not at the end.
We handle every Apple and Google review iteration until your app is approved, at no extra cost, no extra timeline.
Any bug we shipped, we fix on our time. No retainer required.
If we miss a confirmed milestone date by more than one week without a scope change on your side, the next sprint is on us.
A clear view of who we serve well, and who would be better served elsewhere.
We are Ruji, a custom mobile app development company based in Paris. We work with a focused portfolio; every app in our case studies is one we built end-to-end and that runs in production today.
Our clients sit across the United States and Europe; healthtech, edtech, B2B SaaS, and consumer products. Async communication is the norm, responses are fast.
10+ years
shipping production iOS and Android apps
25+ apps
live in the App Store and Google Play today
Senior-only
every engineer on your project has shipped at least one production app
US business hours
online 9am to 4pm Eastern Time, Monday to Friday
Top-rated
4.9/5 across Sortlist and Google · 35+ reviews
Read independent reviews on Sortlist.
Everything you would normally ask on the first call.
Monday to Friday · 9am to 4pm Eastern Time
That is 3pm to 10pm in Paris. Your morning standup is our afternoon. Your urgent end-of-day decision is our early evening.
Slack and Discord channels with response within 2 business hours, US time.
30 minutes on Calendly. Bring whatever you have; a spec, a Figma, a working prototype, or a problem statement. You will leave with a clear technical read on the project, regardless of what you do next.
You will talk to a senior engineer, who will come back with a clear technical read and a scoped proposal if it is a fit.