Tripwire Interactive is a video developer based in Roswell, Georgia.
They originally formed to created Red Orchestra: Combined Arms which was a total conversion mod for Unreal Tournament 2004. They soon made a retail product out of it, called Red Orchestra: Ostfront 41-45 after making a deal with Valve about releasing it on Steam.
Next they came into contact with Shatterline Productions who had also made a total conversion mod of Unreal Tournament 2004 with the original Killing Floor mod. Killing Floor then became a Tripwire Interactive franchise and they released the first retail version in 2009.
Sequels to both Red Orchestra and Killing Floor soon followed, along with publishing other games like The Ball, Dwarfs!?, and Zeno Clash.