SourceForts is a Half Life 2: Deathmatch mod where Combine and Rebels face off in capture-the-flag action with a big twist. Players build bases and other structures with blocks and plates in the "build phase" to protect themselves and their team's flag (which is actually a ball), and then duke it out and try to capture the enemy's flag in the "combat phase". Once the combat phase has ended, it's back to build, where players can repair, improve, and change their creations to ready them for the next combat phase.
A very fun and addicting experience that I much prefer over HL2: Deathmatch.
The creation of forts using the blocks you are given challenges the mind to go wild and create what ever the user wishes. Because of this, source forts is never the same game twice. There's always new strategies to try out within each map.
It's disappointing to see almost all textures reused from Half-Life 2 in these maps however. I understand it's based in the same universe and can't really complain but more original textures and maybe even character models would make this mod stand out from the rest of the Half-Life based mods out there.
With that said, it has been a long time since I last played the mod so it could have improved on my outdated impression.
In the end, it's worth the time investment but from what I gather from various people on the mod's main page, there seems to be no servers which is a shame. :(