All decompiled .ysc game scripts as of GTA V build 2628 (GTA Online 1.60), including native tables. Note that this is a git repository, so there is a history, if you want to look at older scripts.
OpenIV for GTA 5 is a necessary PC modding tool without which you can't really install a number of mods. It was originally designed for Grand Theft Auto IV, which explains the name, but it also works ...