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.
This mod is one of the finest that I've played. Not only is building forts fun (especially with friends), but the combat is pretty fast-paced as well.
You get plenty of time to build your fort, and a nice variety of classes to choose from (reminds me a little of Team Fortress), and was a refreshing mod to play compared to some of the recently released ones.
The downsides:
On the servers that I joined, there was at least one "Griefer" - People that purposely mess up what you are attempting to build or alter your current objective to break your fun for their own satisfaction.
Also, when there are lots of people on a team, you quickly hit the prop limit and can't build quite the amazing base you want to build. (However, if you do have a team that can work well together, you can still pull it off)
Overall, I would give this mod a 9/10 for smooth gameplay, it's unique, and is easy to get on and play for hours on end. The only thing preventing a full 10/10 is the amount of griefers and the prop amount issue.
Other than that, a fantastic mod! I would recommend it to anyone looking for something new to try!