Natural Selection (NS) is a modification for the video game Half-Life. Its concept is a mixture of the first-person shooter (FPS) and real-time strategy (RTS) game genres. The game was created by Charlie "Flayra" Cleveland, who later founded the company Unknown Worlds Entertainment. Natural Selection v1 was first publicly released on Halloween 2002, and is now at version 3.2. Natural Selection 2 was released in late 2012. The game was, in 2008, one of the ten most played Half-Life modifications in terms of players, according to GameSpy.