First released on 2010, February 10, the Sonic Games Development Kit has been a collected code source for anyone in the Sonic fanbase at large to develop their own 3D Sonic the Hedgehog fangame.
So, Sonic GDK, starting with a bit of history.
I've been looking to make sure and apparently no one except a few people are talking about this in a general thread or status update and considering that GDK is fanmade I felt it belonged here.