Description
Killing Floor is a Co-op Survival FPS taking place in the devastated cities and countryside of England, after a series of cloning experiments for the military goes horribly wrong. You and your friends are members of the military and police, dropped into these locations with a simple mission: survive long enough to cleanse the area of the failed experiments.
The only problem is, these "experiments" aren't waiting to be taken out - they´re coming for YOU!
Features:
- 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
- Slow-motion “ZEDtime” to better watch those crucial and violent creature deaths, even in multiplayer
- Solo game mode for offline play
- Nine different monster types trying to eat your face off, armed with everything from teeth and claws, to chainsaws, chain-guns and rocket-launchers
- 12+ 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
- 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 SDK for the creation of new levels and mods
Steam 
Windows 
How to activate your Steam key?
1. Open your Steam client. (If you don't have a Steam Client, you can install from here https://store.steampowered.com/about/)
2. Sign in to your Steam account. (If you don't have a Steam Account, you can create from here https://store.steampowered.com/join/)
3. Click “ADD A GAME” button which is at the bottom of the Steam Client.
4. Now select "Activate a product on Steam..."
5. Write or copy-paste your Steam key which you purchased from Gamesforpc.
6. Now your game is in your library.
7. Find your game in your library, select and click install to start your download.