What is "source engine" etc. ???
I'm guessing it is some sort of open source FPS mod game thing but I never heard of it.
You got some links or something you can link to explaining it?
Sure.
The Source engine is the 3D engine used to make Half-life 2.
Valve gives to players the ability to create their own modification based on their engine.
So, there is a modification called Zombie Master (
http://www.zombiemaster.org), which I am making a multiplayer map for it.
If you own a Source based game, like HL2 or counter-strike source or whatever, you will be also able to play those mods by simply downloading and installing them:
http://store.steampowered.com/freestuff/mods/