Fallout Who
Click to viewThat's a gameplay video for, like, the most videogame mod EVER.
Apparently how it works is that you can find an abandoned UNIT base with the TARDIS inside of it. Once you get it working again, its your to play with. There's more videos on YouTube that go more in depth, but basically you'll get the ability to fly the TARDIS, choosing donations or setting them to random and getting teleported pretty much anywhere on the map. Step out the door and see what adventure awaits...
You can also explore the TARDIS itself, finding cool Doctor Who relics (one of the videos I saw had a hall with pictures of all the Doctor's incarnations) and even a wardrobe with various outfits, so you can even dress like you're favorite Doctor. Plus, you can get a sonic screwdriver, which lets you hack terminals, unlock doors, and overload pesky robots with the greatest of ease.
All that's not even the best part. There's already a sequel to this mod, which adds a universe-threatening crisis that you only have 22 minutes (real time) to fix. Not having played it, I dunno' if that time limit makes it amazing or frustrating, but it sure feels like Doctor Who. Plus, the sequel adds Regeneration, where when your Fallout character is killed, it respawns with a new appearance and different stats.
I've also seen previews for an upcoming mod that features a Dalek invasion of the Capital Wasteland. In that one, it seems you might just run into The Doctor himself.
I wish I had a computer that could run Fallout 3. I've got the XBOX game, sure, but this mod's only available to PC users. Because damn, this all l ooks totally awesome.