http://store.steampowered.com/app/1250/ The game, and all DLC (even individual) is currently 75% off! If you are missing something from your collection or hope to bring a friend in and up to speed before Killing Floor 2, now is the time! On top of that, Killing Floor is also having a free weekend, so you (or your friends) can try before you buy!

• Cooperative gameplay for up to six players against multiple waves of specimens
  
• Persistent Perks system, allowing players to convert their in-game achievements into permanent improvements to their character's skills and abilities
  
• Over 170 Steam Achievements, including “Dignity for the dead” for killing 10 enemies feeding on dead teammates' corpses and “Hot Cross Fun” for finishing off 25 burning enemies with a Crossbow
  
• Slow-motion “ZEDtime” to better watch those crucial and violent creature deaths, even in multiplayer
  
• Solo game mode for offline play
  
• Ten different monster types trying to eat your face off, armed with everything from teeth and claws, to chainsaws, chain-guns and rocket-launchers
  
• 33+ weapons for the players to chose from, ranging from knives and fire-axes to pump shotguns, rifles and a flamethrower
  
• Equip your team with welders, medical tools and body armor to help your odds of survival
  
• Choose which Perks to play with to best balance out your co-op team against the horrors
  
• Open, non-linear play areas: choose when and where to fight — or run; weld doors closed to direct the monster horde down alternate corridors
  
• Fully-configurable, allowing players to change the difficulty level, number of creature waves, or even set up their own favorite waves of monsters
  
• Support for Steam Friends and other Steamworks features
  
• Includes Windows-only SDK for the creation of new levels and mods
  

• OS: Ubuntu 12.04 LTS. fully updated
• Processor: 1.2 GHZ or EquivalentMemory: 1 GB RAM
• Memory: 1 GB RAM
• Graphics: Nvidia. ATI. or Intel GPU with hardware-accelerated drivers Hard Drive: 2 GB free hard drive space

• OS: Ubuntu 12.04 LTS. fully updated
• Processor: 2.4 GHZ or EquivalentMemory: 2 GB RAM
• Memory: 2 GB RAM
• Graphics: Nvidia. ATI. or Intel GPU with hardware-accelerated drivers Hard Drive: 2 GB free hard drive space