I enjoy trying out ideas for web applications and see how it goes.
Bandnews (2004/05), collecting news from the (at the time crazily bad) band websites with a bot.
Blummy (since 2005), in-browser dropdown window for your collection of bookmarklets.
Computerlexikon (since 1999), Fachbegriffe verständlich erklärt. A german computer dictionary.
Colorillo (since 2009), collaborative drawing in the browser.
Factolex (2007-2020), create your own encyclopedia.
Friends Plugin (since 2018), A social network between WordPresses; Privacy focused, by itself a self-hosted RSS++ reader with notifications.
thinkery (since 2011), your brain, organized.
Wizlite (2006), a highlighting marker for the web.