Half-Life: Decay is a Half-Life modification for PC originally created for the PS2 version. The expansion was developed by Gearbox only for PS2. But a recent method of getting files from PS2 allowed a group of Ukrainian developers to port it to the PC. In Decay, there are two main characters, Gina Cross and Colette Green. They are research doctors in the same lab as Gordon Freeman, and they even help prepare the sample and devices for Freeman's experiment. After the catastrophic accident they now must help others within Black Mesa.
In the PC port, you control both characters (or a LAN game can be set up to play with a friend). You switch between characters using the "G" key. This can get very annoying because when you "leave" a character it just sits there doing nothing. The game includes new models, weapons and items as well. Decay features a great story, within the Black Mesa events, which makes it all worthwhile. This is an excellent port of a good Half-Life expansion pack which proves that Half-Life still has a lot to give.