Operation: Harsh Doorstop is the ultimate, free to play, tactical shooter sandbox. Play singleplayer, multiplayer, or co-op modes and explore thousands of community-created maps, weapons, and vehicles via the Steam Workshop. Created by developers of the cancelled Project Reality 2 project.
Task Force is the ultimate tactical shooter sandbox that focuses on close quarters infantry combat. It's made by a small indie team of 3 developers that strive to create exceptional action simulation games.