Halo Zero finished

Last year, several screenshots begat rumors that Halo was being adapted for the Game Boy Advance. In fact, the game was Halo: Blood Covenant, a free fan-made two-dimensional side-scrolling shooter for the PC.

While Halo: BC remains incomplete, another, similar tribute to the Master Chief has now been completed. The French-Made Halo Zero sports similar side-scrolling carnage, pitting the Master Chief against faithful-but-flat re-creations of elites, grunts, and jackals.

Though not endorsed by Microsoft or Bungie, Halo Zero is set on the same planet as the official Halo novel The Fall of Reach and allows "Le MC" to jump and duck, as well as pick up and switch weapons. It is free to download (until Microsoft has it pulled down, anyway).