Half-Life: Decay was an add-on included in the Playstation 2 port of the game Half-Life. Just like the other Half-Life expansions Opposing Force and Blue Shift, this add-on was made by Gearbox. This add-on never came to the PC though, until now. A group of people have ported it to the PC. If you liked the old Half-Life games and want to know more about what happened in Black-Mesa, give this a try! You can download the mod here: Half-Life: Decay Half-Life: Decay was originally a co-operative game. You had to play with two players to finish the game. You can still do this in this port, however you can also play it in single player and simply switch between characters by pressing G. The game is basically the same as the other Half-Life games. You start off, not knowing what's going to happen and then everything goes wrong. You then have to find some weapons to defend yourself from the aliens dropping in.