** VEIN: http://www.facepunch.com/showthread.php?t=1148261 **
A zombie survival RP gamemode inspired by Project Zomboid and aimed at bringing functionality to the roleplay genre by allowing players to actually interact with an environment in a realistic way with damage systems, containers, weapons, and most importantly, zombies. The gamemode isn’t complete though, and there is a lot of content to download. Constantly updated by it’s coder Disseminate.
**DarkRP: http://www.facepunch.com/showthread.php?t=1067488 **
Unfortunately the most popular and overused RP gamemode in Garry’s Mod due to its sheer age and ease of setting up; most gamemodes have used this gamemode as both direct inspiration through emulation, or in the case of making a gamemode that is more fluid and complex. The gamemode itself is good, but the community it has attracted is definitely not. Still updated ocassionally by FPtje.
A gamemode similar to DarkRP with more emphasis on fixing the problems brought up through DarkRP by implementing more functions and features and providing more structure and depth, and allowing users to customize their play style with more freedom. However, this may also cause players to be lost unless the server provides a theme and gives the players a general nudge in how to go about playing it. Not officially worked on, but there will be occasional updates and fixes by it’s coder, Chessnut.
Tiramisu 2: http://www.facepunch.com/showthread.php?t=1166556
A roleplay gamemode aimed at taking down popular HL2 RP gamemodes by actually introducing gameplay to the dull world of super-serious RP without charging its users money, and while giving them the ability to edit and alter the code however they please. The gamemode support(ed) clothing, food, armour, and third/first person, but has stagnated due to its author’s disdain for Garry’s Mod’s admittedly unappreciative and immature RP community. There are some fan made fixes, and Jawalt still does what he can.
Those are pretty much the only RP gamemodes you’ll find that people actually offer support, and that actually work. (for free, as they should be)