About two months ago the project Code for Germany has started with the project Code for Berlin being part of it. Code for Germany is organized by the Open Knowledge Foundation and aims at initiating local groups in all over Germany, that meet on a regular basis to work on open data apps and visualizations for citizens.
I am one of the organizers of the Berlin group. We meet every Monday at 7 at Wikimedia (Tempelhofer Ufer 23/24, 10963 Berlin) and work on different projects, one of them is Bürger baut Stadt. Everyone who is interested, is always welcome to join.