In the IDW Comics series The Other Side, Purgatory (also known as Limana Desperatus and Dark Void of Despair) was a realm where the spirits of the deceased go if they died before the date they were supposed to. They simply wait until it is time to be rightfully judged.
During a bust, Peter Venkman's soul was shunted to Purgatory when his body was stolen by Fred. This was confirmed in "Benedict's Guide to Possession and Exorcism," which says "A soul is displaced forcibly from its living host must quickly regain itself lest it be lost forever to the Dark Void of Despair." Another book suggests it lies between Heaven and Hell and functions as an otherworldly realm of Limbo. Also, as part of a truce between the Angels and Demons, Purgatory must remain neutral in nature and an equal number from both sides guard the borders.
Fred later hired some ghostly goons to kill the rest of the Ghostbusters and dump their bodies in Ecto-1 at the East River. The spirits of the Ghostbusters ended up in Purgatory, where they learn that Peter Venkman possesses supernatural powers due to his body still being alive and that Fred and his cohorts have been making dealings with demons for the souls imprisoned in Purgatory to cross over into the realm of the living.
After the spirits of Elliot Ness, Jelly Bryce, and J. Edgar Hoover appeared to stop the operation, it is revealed that Fred made a deal with Two-Headed Demon, and the deal is that the demon gets to torture Venkman's body for all eternity in exchange for his body being able to enter and survive Purgatory.
Peter Venkman confined the Two-Headed Demon in a Proton Stream set at full power. Winston Zeddemore managed to capture the demon in a Trap before Peter's Proton Pack overloaded. Since the demon was responsible for Venkman's body entering and surviving Purgatory, Venkman starts to suffocate. He manages to get out of Purgatory along with the souls of Winston, Ray, and Egon.
The next week, the Ghostbusters have been restored to their bodies and resurrected. They find and capture Fred's bosses, as he requested before being apprehended by Ness, Bryce, and Hoover.
- In Christianity, Purgatory is actually the neutral equivalent of Heaven and Hell. Deceased people go to Purgatory if they are not pure enough to enter Heaven, but also too pure to go to Hell. Spirits in Purgatory remain in Purgatory until they have spent enough time to redeem themselves for their sins and are worthy enough to enter Heaven. Purgatory is mainly believed in by Catholic Christians.
- While in Purgatory, Winston kills the spirit of a mosquito. This causes Egon to wonder if there are endless levels of Purgatory should an inhabitant die more than once, or if being killed while already dead removes it from the circle of life.
- In The Other Side #2, Ray refers to Purgatory as a karmic Containment Unit and a giant waiting room.
- Ghostbusters: The Other Side
- Teenage Mutant Ninja Turtles/Ghostbusters Volume 2 Issue #1
- Mentioned by Winston on page 4. 
- Winston Zeddemore (2017). IDW Comics- "Teenage Mutant Ninja Turtles/Ghostbusters Volume 2 Issue #1" (2017) (Comic p.4). Winston Zeddemore says: "Could that insulation be Purgatory?"