Contingency Is A Halo Game
As our colleagues at Kotaku (oh God) noticed, a fan made Halo game for PC is in the works. It's called Contingency, it uses Cry Engine 3 and it... has something to do with Halo. It will be non-canon obviously, but it will use Halo game assets as set under Microsoft provisions. That said, the video also says that everything you see is scratch built - maybe this means that the devs were referring to the use of IP?
In any case, if Microsoft doesn't stamp them out - and it has been known to be so hamfisted lately as to leave corpses with "signs of blunt force trauma and a smoky beef aroma" - maybe PC will get a Halo game after all, despite the series being console peasant ground since they ported Halo 2 to Windows Vista.
We can only sit and wait!