A slang term for program. This term was popularized in the 1990s on AOL when kids would create third party programs designed to exploit AOL software. Underground sites would entail the swapping of "proggies" and "punters" like Fate, Havoc, Blue Cross, and MiB. These were designed to paste text macros to disrupt chat rooms, crash other people's computers (and sometimes your own), and cause all other kinds of mischief.
1998: OMG I finally downloaded the proggie Magenta. This is so awesome. I'm going to go act like a cock-sucker in some AOL lobbies until a guide bans my phished account.