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. While SRB2 isn't fully completed, it already
features tons of levels, enemies, speed, and quite a lot of the fun that
the original Sonic games provided.