There's a TF2 "Team Update" doing the rounds at the moment, which has people thinking a new class—guard dog—is being added to the game. It's not. But Valve have still given the concept the thumbs up!
You can check out the user-made concept here, which has the dog acting as a support class, able to carry a harness on its back which can carry weapons, tools and supplies, like a rocket pack, cannons and a...jarate dispenser.
Completely game-breaking of course, but still, a neat way to think outside the box. Even Valve are impressed with the idea, with the creators receiving a letter from Saxton Hale himself, patting them on the back for their efforts.