Super Mario Galaxy 2: The Green Stars is a hack that changes the locations of all 120 Green Stars and all 49 Comet Medals in Super Mario Galaxy 2. It also changes some Prankster Comet stars and all of the World Map layouts are changed as well!
Retro Super Mario Bros. Wii is a hack that changes all 77 levels in New Super Mario Bros. Wii into levels from Super Mario Bros. (NES), Super Mario Bros. 3 (NES), Super Mario World (SNES) and New Super Mario Bros. (DS). The hack does not have checkpoints, but the levels are all easy (because they are from older Mario games).
The Speedy Simpsons Mod is a hack that changes all 49 Story Missions, all 7 Bonus Missions and all 21 Street Races in The Simpsons Hit and Run (PC version). The hack changes all missions to make them feel different from the original game, while retaining the original game's storyline.