A 3D Sonic fan game based off of Doom Legacy (aka "Sonic Robo Blast 2")http://www.srb2.org
Sonic Robo Blast 2 is a 3D open-source Sonic the Hedgehog
fangame built using a modified version of the Doom Legacy
port of Doom. SRB2 is closely inspired by the original
Sonic games from the Sega Genesis, and attempts to recreate
the design in 3D. It features tons of levels, enemies, speed,
and quite a lot of the fun that the original Sonic games provided.