Not a lot is known about this fan game, but many who have played say it is an excellent example of how a SFG should be done. Devios Games has a demo of Sonic Madness at the SAGE booth (available through the Media link above.) He also has posted a list of what to expect for the full edition:
-7+ Massive Levels, each with 3 acts!
-Full mp3 soundtrack from top remix artists like Jivemaster and Malcos!
-Dynamic Rain and Snow Effects!
-Stunning set pieces and death defying stunts!
Can he deliver? We will see soon.