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App development

Apps that reliably work in everyday use.

We build iPhone, iPad and Mac apps with Swift and SwiftUI — production-ready, data-frugal and with an interface that holds up in daily use. From the first idea to the App Store and beyond.

Discuss a projectSee our app in the store

What we do

From the idea to a well-kept app

Consulting & concept

We clarify what your app must do — and what it shouldn't. An honest take on effort, platforms and a sensible feature set.

Native development

Swift and SwiftUI on the Apple platforms: fast, accessible, maintainable. No web containers, no compromise frameworks.

Privacy & performance

Data frugality as standard, smooth operation as the goal — both designed in from the start, not bolted on.

Publishing

App Store submission, review process, metadata, in-app purchases: we get your app cleanly into the store.

Ongoing development

After release it continues: new features, iOS updates, maintenance — plannable and personally supported.

Internal tools & AI apps

Tools for your team, customer apps or AI-powered features — including local, on-device AI.

Why Coolblack

We build products ourselves — not slides

The Coolblack phone agent is our own App Store app: on-device AI, telephony, in-app purchases, push, GDPR — all built in-house and running for real. That experience feeds straight into your project.

  • Our own App Store apps — from the voice agent to a game
  • 38+ years of Apple-platform experience
  • Short paths: you talk to the developer directly
  • Clear quotes instead of agency overhead

Our apps

What we ship ourselves

Ten apps on the App Store, from the phone assistant to games – all from one house, all in real use.

Coolblack KI-Telefonassistent

Picks up when you can’t: captures requests, books appointments and even makes calls for you. No subscription – try it free for up to 60 minutes.

Erledigo

Your agent makes the call for you: doctor, garage or hairdresser appointments. Say what you need – Erledigo picks up the phone.

Boti

AI chat and app workshop in one: describe an idea by text or voice and try the finished mini app right on your iPhone.

Tolki – Offline-Übersetzer

Your offline interpreter for the trip: download languages before you go, then translate conversations, texts and photos without internet – and speak and practise holiday phrases. Free to start, languages from €0.99, all of them for €5.99 – no subscription.

See all apps →

References from our own house

What we built in 2026. All of it in real use.

Seven chapters since spring. Much of it ran in parallel, all of it you can try yourself.

  1. 2026

  2. April 2026

    Tolki

    The offline translator on the App Store.

    19 languages entirely on the iPhone: speech recognition, translation and voice output without internet, without a cloud. Now at version 1.4.

    tolkioffline.com ↗App Store ↗

  3. June 2026

    Coolblack Voice Agent

    On the App Store.

    On the App Store since 9 June 2026: in the “Local” tier, language model, voice and knowledge base run entirely on the device. No server, no subscription.

    Voice Agent →App Store ↗

  4. June and July 2026

    Many small projects

    Boti, BootAIS, Wizard Scorer, Abyss, Eclipse.

    Boti, the AI chat and app workshop on the iPhone. BootAIS, live boats on your map. Wizard Scorer, the score keeper for the card game. Plus the games Abyss and Eclipse.

    Boti ↗BootAIS ↗Wizard Scorer ↗Abyss ↗Eclipse ↗

  5. August 2026

    Erledigo

    The agent that makes calls for you, on the App Store.

    A doctor's appointment, a table at the restaurant, a message to pass on: your agent calls and speaks with a natural voice. Version 1.1 since 8 September.

    erledigo.app ↗App Store ↗

  6. August 2026

    Coolblack Voice Agent

    Version 3.0: conversations that sound real – and an agent that calls for you.

    On the App Store since 25 August: the premium tier holds real conversations, speech to speech in an EU data centre, 21 voices in German and English. And on request the agent makes the call itself, finds the number and delivers what you told it.

    To the app →On the App Store ↗

  7. August 2026

    forge-cmix v2 · data compression

    Making the impossible real: 1,000 MB down to 109.54 MB.

    A 1,000 MB Wikipedia dataset, packed without loss, every byte comes back. 1.13 percent smaller than the fx2-cmix reference from 2024, submitted to the Hutter Prize on 29 August. Data compression is one of our strengths, so MailFundus had to follow.

    Result on GitHub ↗

  8. September 2026

    MailFundus and Fipsta

    Two apps on the App Store.

    MailFundus Archive for the Mac, since 9 September: mailbox empty, everything kept, found instantly – now at version 1.1, free up to 500 messages, full version 29.99 euros. Fipsta for the iPhone, since 13 September: ideas in, video out – now at version 1.2.

    MailFundus ↗On the Mac App Store ↗Fipsta ↗On the App Store ↗

  9. September 2026

    Visitap

    Scan business cards. Keep your promises.

    On the App Store since 28 September: scan a card, check the recognised details, save the contact – plus meeting notes, follow-up tasks and a trade-show mode for events. From trade-show contact to promise kept.

    On the App Store ↗visitap.de ↗

That experience feeds straight into your project.

Discuss a project

Let's talk about your app.

In a free initial call we clarify the goal, the scope and a realistic path to a first version.

Request a call