Hi Ralf,
Great idea. I suggest you have a look at Kanboard if you don't want to develop a full Kanban management system.
It is an open source PHP project which already has an OAuth2 plugin if you want a Moodle integration.
We use it in my university and the ones who use it love it, especially professors with their students, although it is still separate from Moodle in our case.
Good luck!
Max