Black Isle Studios Fallout 3, code named "Van Buren" was to be the third installment of the Fallout series but it was never finished because thrice-cursed eternally damned Interplay fired all the developers on December 8, 2003 for no apparent reason. While in many ways deviating from the original two games, in my opinion it showed more promise than what Bethesda is cooking up right now - just my own personal 0.02$ of course.
Thanks to the great guys over at No Mutants Allowed (NMA, a huge Fallout fansite), we now not only have a video of the unfinished game, but a pre-alpha playable demo as well. This demo is apparently very basic, with a lot of features not or still only rudimentarily implemented. There's no turn-based combat yet, only crappy real time, and a lot of things look unpolished. But still, here it is:
Van Buren playable demo - Guide & Info
Van Buren demo video
Wikipedia Entry on Van Buren
No Mutants Allowed Fallout Fansite
Again, thanks to NMA for this little gem!