We're trying to get active on BG2, a free mod for any Source game past 2007. Specifically it uses the Source SDK 2007. If you have TF2 it works, if you have L4D2 it works. You can also download the tool itself alone if you want. The link to the mod is here: http://www.moddb.com/mods/battle-grounds-2

A guide for installation is here: https://www.youtube.com/watch?v=de6jIS-4qkY