4eBusiness GmbH – home

Our own projects

Alongside our client work, we develop and run products of our own – with the same technologies, processes and quality standards. In live operation, they show how our services fit together: from the idea through design and development to hosting.
Native appsWeb apps & PWAAI in productionHosting & operationsMultilingual

We use what we recommend

With our own products, we carry the full responsibility: for concept, design, development, operations and further development. Every technical decision is one we have to maintain, run and pay for ourselves in the long run – shortcuts come back to bite us right away.

That is exactly why they are our most honest reference. Technologies we recommend to our clients are in production here – and whatever proves itself flows straight back into client projects.

Inventary app (German interface): the kitchen with tags the AI suggests for a photo of the cutlery drawer
Inventary app (German interface) in guest view, with search and info pages such as Wi-Fi, house access and house rules

Our own product

Inventary

The digital guest guide for vacation rentals and home exchanges

Where is the vacuum cleaner, what's the Wi-Fi password, how does the coffee machine work? With Inventary, hosts record their home room by room. Guests find everything via search or by simply asking – in their own language.

From the product idea and the subscription model to day-to-day operations, everything is in our hands.

platforms: iOS, Android and web
3
languages with automatic translation
12
hosting in Europe, GDPR-compliant
EU
inventary.io

Our services in action

  • Software & App Development 

    Native apps built with SwiftUI and Jetpack Compose, a React web app and a Rails API behind them. One subscription works on every platform – billed through Stripe, the App Store or Google Play and verified on the server.

  • AI & Automation 

    A language model recognises items in photos, translates content and answers guest questions solely from the host's own entries – citing its sources. Access details such as Wi-Fi passwords never reach the model. A hybrid search finds things even under a different name.

  • UX/UI & Product Design 

    Two audiences, one app: hosts maintain their property, while guests need neither an app nor an account – an invite link or QR code is enough. Twelve languages, including right-to-left Arabic.

  • Operations, Hosting & Cloud 

    We run Inventary ourselves: containerised with Docker and Kamal, shipped automatically via GitLab CI. Error monitoring, analytics and even the map tiles run on our own infrastructure instead of third-party services.

  • Visibility & Growth 

    A fast, static marketing website built with Astro in four languages, with automatic language selection and cookie-free analytics.

Tech stack

Apps
  • Swift & SwiftUI
  • Kotlin & Jetpack Compose
  • React & TypeScript
Backend
  • Ruby on Rails
  • PostgreSQL & pgvector
  • GoodJob
  • Typst
AI
  • Gemma (open-weight LLM)
  • SAM 2.1 in Rust
  • Multilingual-E5
Operations
  • Docker & Kamal
  • GitLab CI
  • Hetzner
  • Sentry & Umami
Stundenplan-Digital in the browser: a weekly timetable with colour-coded subjects, with the public holiday on Thursday left out
The web app's start page on a smartphone: holidays, calendar subscription, one link for the class and print designs

Our own product

Stundenplan-Digital

The school timetable as a calendar subscription – holidays already in

One parent enters the class timetable in a few minutes and posts a single link in the class group – and every family has the timetable in their Google, Apple or Outlook calendar. School holidays and public holidays are already left out, and changes arrive automatically.

Free, with no account, no app and no third-party tracking.

German states with school and public holidays
16
languages, including Arabic
10
third-party trackers
0
stundenplan-digital.de

Our services in action

  • Software & App Development 

    A React web app built as a progressive web app, and a Rails API that generates subscribable iCal feeds. Every lesson is its own event with a stable ID, so a single lesson can be changed without breaking the series. Contract tests ensure that browser and server produce identical calendar data.

  • AI & Automation 

    A nightly job fetches school and public holidays for all 16 German states from open data sources and checks them against a second source. The illustrations for the print designs were created with generative image AI.

  • UX/UI & Product Design 

    Designed for parents, not IT professionals: sign-in by email link instead of a password, drag-and-drop editing and twelve print designs for the fridge and the kids' room.

  • Operations, Hosting & Cloud 

    Hosted in Germany with Docker, Kamal and GitLab CI. Captcha, error monitoring and analytics run on our own infrastructure – without third-party tracking services.

  • Visibility & Growth 

    A marketing website built with Astro in ten languages, with a strict content security policy and no external requests. Shared links show preview images rendered on the server – key to spreading through class groups.

Tech stack

Frontend
  • React & TypeScript
  • Vite
  • Tailwind CSS
  • PWA
  • Astro
Backend
  • Ruby on Rails
  • PostgreSQL
  • Solid Queue
  • iCalendar (.ics)
Operations
  • Docker & Kamal
  • GitLab CI
  • Cap (captcha)
  • Sentry & Umami

Have a product idea?

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