Pokemon Luola is a good hacking project of Pokemon FireRed that has been started a long time ago.
PokeScape is a hack of Pokemon FireRed which let you become a new Pokemon Champion of the whole world.
Pokemon FireRed: Immersion is a customized hack of Pokemon FireRed we usually see.
Pokemon Caelus will tell you the story of Finso Region. It is a hack made from Pokemon FireRed.
Pokemon Stupid Version is a hack of Pokemon FireRed, but without too many changes from the author.