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"Valve and Tripwire Interactive have announced that Killing Floor is now available for pre-order on Steam. Those who pre-order the title before its May 14 release will receive a 25% discount, knocking the price down to a cool $15.00. In addition to the pre-order announcement, a new trailer has been released showcasing the titles zombie-killing action. The game looks to combine some of our favorite shooter features, including six-player co-op and a persistent perk system. Oh, and zombies. Can't forget the zombies."^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.engadget.com/2009/04/30/25-off-killing-floor-pre-orders-on-steam-new-trailer/>