Fans of certain blue Hedgehog in the modding community have brought over Sonic Unleashed to the PC, not sure why but they did it.
Sonic Unleashed had originally been release on the Nintendo Wii, XBox 360 and PlayStation 3 systems but had not been received with much praise by critics or fans. In the new mod you get access to the Unleashed levels without the terrible plot or that stupid Werehog.
Using a modded version of Sonic Generations, those crazy people have created a free version of Unleashed with improved graphics and that runs at a smooth 60FPS.
Sources: Rock, Paper, Shotgun