STH3D is probably my longest running project ever. I started it years ago when I was a Sonic fan and since then it was improving. Most of the time I'm working on the game alone, but I wouldn't complete it without help of my friends. I also want to mention a great fan game called Sonic Robo Blast 2, which was inspiring me a lot during these years.
The game is made on an classic Build engine by Ken Silverman and it uses the EDuke 32 port. The game is free and you can run it on Windows, Linux or Mac. You can also play it with joystick, thanks to the extensive configuration. Hope the fans of Sonic games and indie platformers will enjoy STH3D. If you have any problems with the game, just PM me and I'll try to help.
Good luck and stay tuned for more updates!