Natural Selection 2, the sequel to the popular Half-life mod, Natural Selection, was the most popular independent Half-life mod that was played by over 300,000 players, is now available for pre-order on Steam, developer Unknown Worlds has announced.

Natural Selection 2 is a online-only FPS/RTS hybrid where gamers can play as marines, aliens or commanders and fight in atmospheric sci-fi environments. Whether you play as one of the elite marine Frontiersmen or the vicious alien Kharaa, you must use unique strategies and your abilities to win. Marines form persistent squads to find and destroy alien hives. Aliens can choose a wall-running Skulk, pudgy Gorge, flying Lerk, murderous Fade or gigantic Onos that can smash through doors.

Those who pre-purchase Natural Selection 2 now will be upgraded to the Digital Deluxe Edition for free. The Deluxe edition includes, the Natural Selection 2 soundtrack (almost 1 hour of music, a digital art book (40 pages), exclusive wallpapers and avatars and an exclusive in-game marine model.