This is the work of mapmakers Hypixel and SethBling, who have incorporated all of TF2's eight classes and built a mechanic that allows you to switch from one to the other. There are also ammunition packs and medkits scattered about, just as you'd expect, and all your favourite control points to fight and die for.
Best of all, you won't need to download any mods to get started, although you will need the 12w37a snapshot, so let me link again to our handy guide on how you can make that happen. Once you've done that, your only real challenge is finding an empty server. Until Minecraft gets a better server browser, the best place to start is among the comments on this Planet Minecraft thread. Enjoy.