App development

An app agency in Cologne — since 2009

We specialise in apps that are scalable, business-critical or close to the hardware, and that have to meet serious security requirements. From start-up to corporate, for iOS, Android and Flutter.

Native apps for iOS and Android, cross-platform with Flutter
Professional UX/UI design with clickable prototypes
Backends, IoT integration and operations from one team

What we build

We have been designing and building bespoke apps since 2009, covering the whole chain — ideation and UX design, front end and back end, operations and maintenance.

Our strength is applications that have to hold up: car sharing for millions of users, a ticketing backend calculating prices on the fly, a surgery manager running in a clinic.

Why it is faster with us

Because we do not start from zero. Fifteen years of project work produced ApptiveGrid — our own platform for the data, forms, approvals and reporting that sit behind most apps.

For your project that means the standard parts already exist. We build bespoke where it makes a difference, and reuse where it does not.

App services

From sketch to go-live

Consulting & concept

We are your partner before the first line of code. Together we settle the requirements and decide on delivery, scaling and market entry.

Design & UX/UI

From the first screen design to a clickable prototype. Design and user experience decide whether an app gets used — not just installed.

Development & testing

The current state is available at any time, tested automatically and by hand. You see progress instead of hearing about it.

Project management

Agile methods and short feedback cycles keep the project on course, with one contact across every phase.

Operations & support

Our responsibility does not end at go-live. We run and keep developing your app.

App analytics

Usage data shows what is actually needed, which lets us validate concepts before building them.

Project phases

How a project runs here

Phase 1–3 · Understand

Kick-off workshop, requirements analysis, concept. What comes out is what gets built and why — not just a list of features.

Phase 4–5 · Build

Design sprint, then development in sprints. We launch an MVP first and extend it with updates, rather than building in the dark for a year.

Phase 6 · Operate

After release, maintenance and further development keep the app current — including when iOS and Android move underneath it.

Apps we have built

Karlsruher Verkehrsverbund

KVV-Homezone

Smart Travel With KVV Homezone

iOS
Android
Web
flutter

Deutsche Bahn Connect GmbH

Flinkster Carsharing

Germany's Largest Carsharing Network

iOS
Android
Mobile
Mobility

Rheinwerk Verlag

SAP Press Reader

Custom Book App

iOS
Android
Mobile
Tablets

See all projects

What clients say

„Mit ZWEIDENKER sind wir innerhalb weniger Wochen vom ersten Gespräch zum gewünschten Ergebnis gelangt. Die Zusammenarbeit war unkompliziert, professionell und sehr zuverlässig. Wir wurden rundherum, also in Sachen PM, Konzeption und Umsetzung äußerst kompetent betreut.“

Marvin Kassühlke Product Owner, bloXmove

„Besonders hat sich das ZWEIDENKER-Team durch kurze und unbürokratische Kommunikationswege und eine flexible Arbeitsweise ausgezeichnet. Aufgrund der fundierten Expertise im Bereich App-Entwicklung haben wir gemeinsam eine tolle Lösung für unsere Förderer entwickelt.“

Professor Dr. Wolfgang von Keitz Vorstand, Iran-Darbandi-Stiftung

„Wir haben mit ZWEIDENKER einen zuverlässigen Partner gefunden, mit dem die Arbeit als agiles Team sehr viel Spaß gemacht hat. Vielen Dank für die großartige Zusammenarbeit!“

Simon Woker Product Owner Mobile Apps, Deutsche Bahn Connect GmbH

„Neben der offensichtlichen Expertise in der App-Entwicklung hat uns das ZWEIDENKER-Team besonders mit fundiertem Wissen und Erfahrungen in der Mobilitäts- und Transportbranche beeindruckt. Dieses Fachwissen und der agile Entwicklungsprozess ermöglicht die Umsetzung eines bisher deutschlandweit einzigartigen und innovativen Projekts im Bereich Tarifentwicklung.“

Stefanie Herrmann Leiterin Tarifmanagement, Karlsruher Verkehrsverbund GmbH (KVV)

Quotes shown in the original German.

Frequently asked questions

How long does it take to build an app?

It depends on scope and complexity. A minimum viable product takes 1–3 months, an average app 3–9 months. We launch an MVP first and extend it with updates.

What does app development cost?

It depends on the features, the devices to support and a number of other factors. Custom apps typically start in the five figures. If your plan comes down to data, forms and approvals, a solution on ApptiveGrid is usually considerably cheaper and faster — and we will say so in the first conversation.

What is included in the price?

Detailed consulting up front, concept and programming, regular demo versions during implementation, final testing, and publishing to the respective store.

Native app, hybrid app or progressive web app?

It depends on the features and the devices. To bring an existing website to mobile, a progressive web app is often enough. For device-specific functions, offline availability or push notifications, native or Flutter is the right call.

Which platforms do you develop for?

iOS, Android and Flutter on the front end, Pharo on the back end. For cross-platform apps we have relied on Flutter for years — KVV Homezone runs on iOS, Android and web from one codebase.

What do you need from us?

For the first conversation, a description of the problem is enough — no specification required. For a firm quote we work out together which features belong in scope, in a requirements workshop if that helps.

At what point can you help?

From the idea to the finished product. Depending on how far planning has come, we advise on requirements, concept and design — or step straight into delivery.

Let's talk about your project.

Tell us what needs building. We will say honestly what has to be built from scratch and what does not.

Discuss your project Or look at ApptiveGrid yourself