ASI Loader is the tool that loads custom libraries with the file extension
.asi into the game process. There are several ASI loaders made for different GTA games:
The idea of the ASI loader comes from Vice City, the sound engine of which ( ) has native support for plugins made as .asi libraries. So, in Vice City and GTA III asi files could be loaded easily just by putting them into the game folder with no external tools needed. GTA SA and GTA 4 do not have such a feature, so the ASI loaders were made.