Since its release in 1998 there are literally hundreds of different mods for Half Life. Half Life has an excellent multiplayer capability and a majority of the mods are for online play. Virtually all of them have started out as fan created mods of which some have become full retail games such as Counter Strike and Day of Defeat.
If you looking on information for a particular Half Life mod that is not listed, please drop me an email and I'll try to get some information. I'd also suggest searching the Internet, there are dozens of Half Life fan sites that have links and information on many other full game mods.
