Mann vs. Machine - The Sound of Medicine
The Two Cities Update is available November 21st, 2013. Mann vs. Machine lets you and five friends fight a lethal horde of robots on new maps, with the opportunity to upgrade abilities and weapons along the way. Go to http://www.teamfortress.com/twocities/rottenburg for more information.
Available on Steam: http://store.steampowered.com/app/440/