UPDATE: This has been proven to be a fake. The author of the screenplay has e-mailed us to say that he had sent the script out with "the hope that someone would run with it" and to get feedback on his writing.
"I apologize to Gene and Lee (and Dan, Harold and Ivan) for the complications that may have arisen from the posting of this script that I'd written. Once again, I did not expect the amount of coverage it's received, and I consider it an honour to hear so many positive reactions to something that I'd written. I'm sorry to have wasted people's time, and I hope all the best for the future of the franchise."
Before director Paul Feig took the reigns oo the Ghostbusters franchise and decided to completely reboot it, there were . . . many scripts for the ill-fated GHOSTBUSTERS 3. Towards the end, The Office scribes Lee Eisenberg and Gene Stupnitsky were the last to work on the script when it featured the original cast. The most recent leak represents an iteration of that script where Egon was very much a presence in the story (before Harold Ramis' passing, of course). You can read a lot more details on the actual script here, but it essentially delivers all the staples you'd expect to find in a GHOSTBUSTERS film.
To give you a taste of what might have been, the original Ghostbusters have been all but usurped, serving more as supervisors to newbies in what's become a very commercialized business. Why's that? Property damage, for the most part. Now the company is run with more high-tech equipment that avoids the classic proton packs altogether. The new CEO, Todd, is evidently a real douche canoe (he keeps Slimer locked up as a trophy). Oscar (Dana's son) is now a Ghostbuster who stays tight with the OG crew. Venkman's walked away from the business and has become mayor in the process. As far as the baddie, well, an apparition with tall, pale features and no face keeps popping his head around the city and attacking at will. This spirit as finally identified as Wolfram Von Grauen, who was head architect at the Chicago's World Fair of 1893. The man sacrificed hundreds of people during his life before being commited to an aslyum. As the story goes, the old Ghostbuster crew finds themselves getting back together and newer, more destructive proton packs are realized. The end culminates in a giant battle with a spirit Von Grauen conjures from the sea. Much like the first film, the original Ghostbusters must cross the streams, but this time . . . they don't make it. In the film's coda we find the Ghostbusters playing cards in their ghost form at the station. FIN.