SADX Hacks

Super Sonic fix - Makes Super Sonic's textures always load, preventing crashes when using Cheat Engine or the Trainer.

GC SET files - Object layouts from the GameCube version of SADX, with more background objects than the PC version.

Metal Amy Adventure DX - Replaces Sonic with Metal Amy, who has different abilities than normal. Topic on Sonic Retro forums

SA2 Hacks

Super Sonic hack - Loads Super Sonic instead of Sonic.

Alternate Character hack - Loads the alternate characters in 1P mode.

No Battle hack - Loads the original Dreamcast intro, title screen and menu backgrounds.

Dreamcast Models - Character models and textures from the Dreamcast version, converted for the PC port.

Character Select hack - Allows you to load the character of the opposite aligment by holding L, and the 2P alternate by holding R.

Character Select hack (alternate) - Allows you to load any character by holding buttons on the controller.

Sonic 2 Hacks

Not-so-Super Sonic 2 - A hack with stuff, including Amy Rose. Currently not being worked on.

S2Boost - A Sonic Rush style boost in Sonic 2.

Sonic 2 Secret Rings edition - A hack adding missions similar to Sonic and the Secret Rings. Topic on Sonic Retro forums