Killing Floor is a cooperative first-person shooter video game developed and published by Tripwire Interactive.

The perk, similar to the idea of a character class, provides bonuses towards certain weapon types, armor, movement, and other factors.

For example, the "Sharpshooter" perk, which provides accuracy benefits when using scoped rifles, can be raised in level by completing a number of headshots with specific weapons.

Alex Quick, the lead level designer and texture artist, stated that "there are a whole bunch of ideas on the drawing board that we can add in after launch, including the 'Story' mode from the mod, for instance.

Horzine Biotech, a biotechnology company, is contracted to conduct experiments of a military nature involving mass cloning and genetic manipulation.

Despite the best efforts of the local police, the civilians are quickly overwhelmed and consumed by the seemingly endless supply of clones now streaming from the gaping maw of Horzine Biotech's headquarters.

Having escaped their sterile prison, the creatures begin to fan out to neighboring areas, devouring the helpless citizens of London while the Metropolitan Police fruitlessly attempt to fight back.

Desperate to contain the outbreak from reaching overseas as planned by the mutated and cybernetically enhanced scientist Dr. Kevin "The Patriarch" Clamely, the British government quickly begins to organize ragtag teams of surviving British Army soldiers and Special Branch police officers to fight back against the hordes of mutated "specimens."

[21] During the PlayStation Experience event in December 2014, Tripwire Interactive announced that Killing Floor had sold almost 3 million copies on PC.

[18] GameSpot commented that the game graphics compared poorly with contemporary shooters, and that the voice acting was bad, but considered that the sound effects were very good, and that despite its flaws, "you can't help but enjoy it.

"[19] Some reviewers also considered that the lack of any real plot or aim for the players other than killing specimens, the small number of existing maps, and the repetitiveness of the gameplay reduced its replay value.