After 17 years in development the famous Half Life 1 co-op mod has finally made its way to Steam and you can grab it right now for a low, low price of nothing. You don't even need to own Half Life 1 to play through the campaign with 10 buddies in tow.

Even though the ability to play Half Life 1 with friends is a major draw for Sven co-op it is the 17 years worth of custom game modes and maps that should excite you the most. Here's a short trailer showcasing what exactly is possible with Sven co-op:

If you're worrying that the Half Life campaign is going to be too easy with a couple of buddies at your side let me just reassure you that it most certainly won't. The more players there are on the "human" team the more enemies there will be and the stronger/more durable they will become. So no matter how many people you can round up for a game you should be adequately challenged.

I haven't played Sven co-op in years, almost a decade, but even back then there were plenty of creative and unique custom maps. Everything from custom campaigns, challenge modes, puzzles, trap/evasion maps, semi-RPGs and I even distinctively remember one map that was some sort of an FPS/RTS hybrid. 

Where I'm getting with all of this is that you should try Sven co-op. The Half Life campaign alone is worth it and the massive library of custom maps will make sure to keep you busy for a very long time. So grab a few friends and give it a bash, it is after all completely free but most importantly, fun.