So what systems could you use for a Ghostbusters game?
Ghostbusters. Well, obviously. Very very out of print, but findable online and new cards and dice available quasi-legally from The Nerdy Show. A classic design that fed into the d6 System, WEG Star Wars, Shadowrun and World Of Darkness. It also contains the only encumbrance rules I have ever successfully used. I like this so much I ran it a lot in high school and last ran it less than a year ago for a group of players who are all younger than it.
It ran with the franchise concept, while also statting out the movie characters as slightly better than starting PCs rather than wildly beyond anything a player could ever hope to get the XP for.
The adventures tended to load jokes into the premise, scenes and NPCs because that’s the only way to ensure amusement at the table, while the film itself got most of its humour from a cast of comedians bumbling into a Call Of Cthulhu adventure. They also had alien invasions in two out of three adventure supplements, which was perhaps too many...
Ghostbusters International. Having produced an elegant rules-light classic, WEG took the second edition in a more traditional RPG direction. Still, the adventures are generally pretty good.
TOON: Witchdusters in Son Of Toon - I ran this on and off for the same high school group as my actual Ghostbusters game, as an outlet for slightly too silly ideas.
InSpectres. “Fighting the forces of darkness so you don’t have to.” A light indie game about a not entirely competent paranormal investigation service, which nearly got its own spinoff film. The reality TV style confessions to camera allow players to frame flashbacks as well as make rambling jokes and blame other PCs for property damage.
Orpheus. A World Of Darkness spinoff game of a ghost hunting and astral projection firm which gets smashed to bits in the adventure series. Plays the premise straight and scary - “James Cameron’s Ghostbusters.”
Hacks! Cinematic Unisystem is a solid choice - looks like David Goodner’s version has fallen off his site but is backed up here in PDF. Cortex Plus has a nice one from Rose Bailey. And since Linneman posted in the comments here, a Black Hack hack.