There is an interesting discussion going on over at the RPG.net forums about using the new Delta Green: The Role-Playing Game rules as a stand-in to run Ken Hite’s magnificent Madness Dossier.
Ken Hite’s Madness Dossier was published in 2014 for GURPS. For those unfamiliar, here is the description given on the forum post:
The Madness Dossier is a different take on cosmic horror. In 535 CE, reality and history themselves were overturned by an unknown disaster. The twist here is that history as we know it was created from that point, and the prior history with a humanity enslaved by Babylonian deities (maybe) and monsters (definitely) was more-or-less erased. In the 19th century, the old history broke through during an archaeological dig, leading ultimately to the creation of Project SANDMAN, a group of deep-black agents, brain hackers, and memetic scientists desperately fighting a war against an enemy that gets stronger as more people know it exists. SANDMAN operates without oversight, behind the scenes, waging a war to stabilize accepted reality and destroy the irruptors at a terrible cost. PKD-esque hidden histories and realities, mind control, and the moral corrosion of the SANDMAN agents are big themes.
If alternate reality horror and modern conspiracy are what you’re looking for in a game, then go check it out.