The official GDG DevFest 2012 Karlsruhe fest app. The official GDG DevFest 2012 Karlsruhe fest companion app supports devices running Android 2. 2+, and is optimized for phones and tablets of all shapes and sizes. GDG DevFests are large community-run events that can offer speaker sessions across product areas, all-day hack-a-thons, codelabs etc.