Private
My own projects. Some are open source on GitHub →.
Apps, tools and add-ins
EdgeNums, the tricky number puzzle
2026
A number puzzle from one C# and Avalonia codebase for Android, iOS, Windows and the browser, with every puzzle checked for a logical solution before release. Each row and column holds every number once plus one empty cell, and the numbers on the edge show which number comes first from that side.
Kickbase Kaderplaner
2022 – 2026
A squad planner for the Bundesliga fantasy game Kickbase. It shows which players are worth selling and how a sale affects the balance and the credit line. It started in 2022 as a Google Apps Script bound to a spreadsheet and now runs in the browser without a server.
Doc2Lib SlotWatch App
2024 – 2026
A service that checks Doctolib once a minute for appointments opening up in a specialty near a location and reports each hit right away over Telegram and mail, with a booking link. It runs several search jobs in parallel, keeps a lockout period per doctor and offers a PWA interface for the phone with a setup wizard. It started as a Google Apps Script bound to a spreadsheet.
Secured List App
2022
A password manager built as a Flutter prototype in Dart, running on Android, iOS, web and Windows from one codebase. The data is encrypted with AES, and the key comes from a passphrase the user enters. Entries are stored either on the device or in Google Drive, so a backup does not need a service of my own.
Stock Quote Add-In for Excel
2007 – 2018
Microsoft once shipped the MSN MoneyCentral Stock Quotes Add-In for Excel, and then it was gone. My add-in is the replacement. It brings stock quotes and FX rates into a worksheet as normal Excel functions, built on the Excel-DNA library. It worked from Excel 2007 through to Excel 2016 and stayed open source the whole time. It is no longer active, because Google shut down the service it pulled the quotes from.
Mindbak – Online Mind Mapping
2008
In 2008 I got the chance to develop a prototype of an online mind mapping tool in Silverlight. It is only a test and proof-of-concept project and somewhat buggy, but the basic functions work.
The maps are edited with keyboard and mouse, and topics can be moved by drag and drop.
Own web platforms before 2006
Netleih.de
2002
Netleih.de was an online DVD rental service with a flat monthly fee. DVDs came by post. I founded it in 2002 and built the website and its back end. The company was sold in January 2003.
Singlekafe.de
1999
Singlekafe.de was an online community for singles with personal ads, photos, chat and matching. I built it in 1999 to learn how to write my own website. The site was sold in 2004.
Open Source
Other open source projects are on GitHub.