Fortress Forever is a nice source engine mod that was released in 2007, a few weeks before TF2 came out.
Since October 13th 2013, the mod became a standalone source engine 2006 game and can now be downloaded for free from the Steam Store.
Link: https://store.steampowered.com/app/2535 ... s_Forever/
Don't forget to join our FF server as well and add it to your favorites: server.maxcommunity.net:27025