Mobile app development agency
Mobile app development agency in Athens.
TWENTYONE is a mobile app development agency in Athens. We design and build iOS and Android apps — the interface, the code, the API behind it and the release to the App Store and Google Play — with one team. A place on the home screen has to be earned; we build the apps that earn it.
The problem
Most apps are a website in a frame
They open on a search box, deliver what the browser already delivered, and are deleted in the spring clean. An app is a different contract: it may know who you are, remember where you left off, speak first, and work when the network does not. An app that earns none of those had no reason to exist.
So the first question in any mobile app development project is whether you need an app at all. Sometimes the honest answer is a faster website, and we will say so — a mobile app development agency that never says it is selling, not advising.
What we deliver
Mobile app development from the first sketch to the store
- Product and UX
- The flows, the screens and the design system, designed for the thumb and for each platform's own conventions — the sheet, the back gesture, the haptics.
- iOS and Android
- Cross-platform in React Native with Expo, or native Swift and Kotlin where the product demands it. One team, both stores.
- The back end
- The API, accounts, payments and push notifications, built in Node.js and PostgreSQL and shared with your website rather than duplicated.
- Store release
- App Store and Google Play listings, review and submission, handled by us — including the privacy declarations both stores now require.
- After launch
- Crash and performance monitoring, staged rollouts and over-the-air fixes — because most of the work in mobile app development starts after launch.
How we decide
React Native by default, native where it matters
For most commercial products — booking, commerce, accounts, content — React Native mobile app development is the right call: one codebase ships to both stores, shares its logic with the website and lets a fix be written once. Native Swift and Kotlin are right for sustained background location, heavy real-time graphics, AR or deep hardware work, and we build native when that is what the product is.
The decision is made in the blueprint, in writing, with the reasons — not by habit.
App and web
One product, not two projects
The most expensive mistake in mobile app development is building the app as a separate project from the website. Two back ends, two sets of business rules, two teams — and within a year the price in the app and the price on the site disagree.
We build both against one API. The same Node.js web development team that runs your platform runs the app's back end, and the same React.js web development team that builds the site shares its types and design tokens with the app. A change is made once and reaches both.
The result
Retention, not installs
An install is a vanity number; the question is whether the app is opened in week six. We build for the returning user — saved details, the one-tap repeat, the notification worth allowing — because that is what makes the second year cheaper than the first.
How we work
How a mobile app development project runs
- Briefing
- You tell us what you are building, what exists already and what is in the way. We reply within two working days — with questions, or with the honest answer that you do not need us.
- Blueprint
- Scope, architecture, the stack and a fixed plan, agreed before a line of code is written. You know what is being built, in what order and why.
- Build
- Designed, built and tested on real iPhones and Android phones, with test builds you install from the first weeks. Working software every week or two, on a staging address you can open, rather than a reveal at the end.
- Launch and after
- Release, monitoring and a named team that stays. The code, the design files and the data are yours.
The record
A mobile app development agency with apps in the stores
We build and run the TRVL AIR app for iOS and Android. 19 years of work for brands including COSMOTE, Piraeus, Avène, MARKET IN, SCORPIOS, TRVL AIR and NEXTCOMMERCE.
Design, engineering, photography and film under one roof, so the app's screens and the imagery inside them are made by the same people.
Common questions
- What does a mobile app development agency do?
- It designs, builds, publishes and maintains apps for iPhone and Android. TWENTYONE, in Athens, covers the whole of it in-house: product and UX design, the iOS and Android app, the API and back end, App Store and Google Play submission, and updates after launch.
- Should we build native or cross-platform?
- For most commercial apps, cross-platform in React Native: one codebase and one team for both stores, with real native components. Native Swift and Kotlin are the better choice for sustained background location, heavy graphics or AR, and deep hardware or Bluetooth work.
- Do you publish the app to the App Store and Google Play?
- Yes. TWENTYONE prepares the store listings, handles review and submission for both the App Store and Google Play, and ships the updates afterwards — including over-the-air fixes where the platform allows them.
- Do we need an app, or is a website enough?
- An app is worth building when users return often and it can do what a browser cannot: know who they are, work offline, send useful notifications or use the phone's hardware. If none of those apply, a fast website usually serves better, and TWENTYONE will say so.
- How much does a mobile app cost in Greece?
- It depends on the scope, the platforms and the back end the app needs, and the cost does not end at launch: store fees, hosting, monitoring and updates continue every year. We price each app after a briefing, and our journal breaks down what drives the cost.
Also from the studio
Further reading
Initiate the blueprint
Tell us what you are building.
The stack, the timeline, the thing that is currently in the way. We reply to every briefing within two working days.