Mari0 is a faithful recreation of the original Super Mario Bros. with some great additions: a portal gun, a 4-player coop mode, a level editor and a portal map pack. For a more detailed description of the game consider to checkout the RGCD Review. It is freely available for Windows, Mac and Linux.
Mushroom Kingdom Fusion is a big platformer project that merges characters and levels from many different gaming series into one game. For example: Mario, Wario, Mega Man, Sonic, Ghouls n Ghosts, Castlevania, Doom, Halo, Contra, R-Type, Zelda, Metal Slug, Ninja Gaiden etc.
Conclusion: A huge and really good fan game!