Right, those mods are activated through the QB Autostart mutator.
As in the difference between zip and rar, those are just 2 common compression formats.
Another one used is ace and 7z (7zip). But zip and rar are the most common formats on BCFiles. WinRar (not free as such) can open most of those (unsure about 7zip, but mods in that format are usually distributed through self extracting programs).