This was a mod for HL and this sequal is a standalone game using a new game engine. This is a Winter special deal so it might not last too long (Looks like only 10,000 are available). When you purchase you will receive two emails with a steam activation code and one can be forwarded to a friend. Once you order you get immediate access to the Beta. The game is a combination of a first person shooter and RTS.
Natural Selection 2 – 2x @ $34.95 = $17.48 each.