Another fascinating take on an old-school mechanic comes in SourceForts. The game here is Capture the Flag, but unlike most games, this lets you defend your trophy in some interesting ways. In this team-based shooter, each game is divided into "Build" and "Combat" phases, something like classic arcade game, Rampart. During the Build phase, you and your team use gravity guns and metal panels to construct a fort to house your flag and stymie your enemies - all while they're doing the same. When Combat starts, storm your foe's base, navigate their construction, snatch their flag and bring it home if you can.

Get SourceForts here.