As a human it’s your job to fend off hordes of undead with whatever weapons you can find (you’re given one random melee weapon and a handgun to start you off). There are two classes – the human survivor and blood-thirsty zombies.Everyone starts out human, apart from one (volunteer or auto-selected) zombie. At the time of writing Zombie Panic! Source is entertaining more online players than a considerable amount of new full-price releases, which is pretty good going for a free mod. If you’ve not got Half-Life 2 you could buy it (it’s about $10, £7) or a similar title with support for the SDK.Luckily there is on the Steam website, choose one you like the look of and make sure it’s downloaded and ready to play. If you’ve got a full copy of Half-Life 2 then you’re already done.

(Steam does work on Mac, as does Half-Life 2 but unfortunately free third-party mods that run on OS X are very thin on the ground).You’re going to need a copy of a game that uses the Source engine and supports third-party mods. Where many developers now charge users for in-house total conversions (Battlefield Bad Company 2: Vietnam, for example) PC have long been able to enjoy similar efforts for free.Here are a few personal free favourites to get the most out of your Source engine games! Full Steam AheadIf you’ve not got Steam, head over to and download the client for If you are afraid to upgrade from Vista or XP because you feel it is completely different to what you are used to, you should read this new guide. Did I mention it's free? Were free to hack and mould the engine into completely different games.Many of these games survived the jump from the original Half-Life engine to the Source engine, first used in Counter-Strike: Source & Half-Life 2 (and re-used several times in games like Left 4 Dead).

Thanks to the free software development kit (SDK) modders, mappers and Completely free, and a tool that has dozens of applications allowing you to try your hand at the challenging world of computer-generated artwork. Advertisement Valve’s original hit Half-Life gave birth to some wonderful third-party development.

Half life 2 multiplayer mods