This modification requires a clean (no mods) GTA San Andreas, but after installing the mod you will be able to play both normal SA and GTA Familier at the same time. Provided that you have Microsoft .NET Framework 3.5 (if not, you will have to install the mod manually, on powerful computers it is included).
This modification brings many changes to the familiar world of San Andreas: -New player -New character models -New passers-by -New weapon -New Grove Street -New loading screens -New storyline of 4 missions (in 0.1 Demo) with cut-scenes and texts.