The creator of this side-scrolling interpretation of Team Fortress 2 entered it in a map-modding contest last year and, for obvious reasons, won the sucker outright.
[Correction] Dylan Loney entered this and won his modding contest. (Here's another top-flight entry.) An earlier version of this story said his entry had missed the deadline.
Steaky says he "plan(s) to finish and release a full version in the future." A quick Google search reveals the guy's built two maps already, (plus this one). I've no idea how far along the project is or how it would be implemented, but it is sure fun to look at, and think about what could be. Go for it, man.
Thanks to Gøran T. for spotting this and sending it along.