There has been a project going on for quite some time, it was a procedure to port over the contents of Grand Theft Auto: San Andreas into Grand Theft Auto IV. Some gamers might question what the purpose of this is, but it basically allows you to do everything you loved about San Andreas but in the amazingly awesome RAGE Engine with Euphoria support. Total conversion modification for the win.
I'm not going to waste a lot of time explaining stuff, so instead I'll just leave you with the basics: You can play the entirety of GTA San Andreas in GTA IV. I don't know if Rockstar would consider that pirating but you'll still need a fresh, full copy of GTA IV before you can play San Andreas. So technically, anyone who buys GTA IV to play the SA mod is still giving Rockstar some sweet, sweet moola.
Enough about the legal ramifications, let's take a look at some gaming goodnesss.
IV:SA³ "World Enhancement" Launch Trailer - Mod DB
Additional features of the mod includes enhanced graphics (duh), draw distance, lighting, Euphoria-based animations and AI reactions, vehicle damage, bullet/gun-physics and the nifty new replay and video editing system provided by the Rockstar Social Network.
I'm curious if this mod will boost sales for GTA IV the way DayZ is boosting sales for Arma II? I guess if the game starts appearing on the top 10 weekly Steam charts on a regularly basis then we'll know for sure.
The trailer comes courtesy of Moddb but the actual game modification and additional details are available over at the Official GTA IV: SA Website.