Thanks to my former colleague @the_qa_guy, I now know the website http://brokeyourapp.com/. The website is presenting nasty bugs in iOS mobile apps.
The team behind the page is checking and testing random apps from the iOS store and is trying to break them. If they broke the app, they write a bug report with detailed steps, screenshots and videos. The whole report will be send to the developer. The bugs are categorized into
- UI Glitch
- Dead End