I'd like to run a cosmic horror game. Not like Lovecraft cosmic horror, but existential "everything we think we know is a lie" sort of personal psychological terror. A game where the players are willing to explore and examine their characters' reactions to assaults upon what they believe reality is.

Example: Typical RPG - Godzilla is scary because he can crush or eat you, and there's nothing you can do to stop him. You are insignificant.

Existential Horror - Godzill is scary because it violates the way biology is supposed to work. It's violence against reality that calls into question causality and every assumption we have; if monsters exist, what else is science wrong about? Also, what about the square-cube law?

Or you can pick other typical RPG tropes that violate our notion of the way the world "should" be. Magic, monsters, etc. Not "unexplained by science", but "violates what we believe to be possible."

There will be typical RPG adventuring as well - problem solving, social interaction, and combat - but the deep internal wrestling with violated worldviews is something I want to emphasize, and that's entirely up to the players.

If this kind of deep RP seems interesting to you, I've got two ideas.

1. The Anomaly. Science Fiction, set in the future. Players are scientists sent into deep space to examine a scientific anomaly that turns out to be much more than a simple curiosity; something with dangerous and maddening implications. Players might also play ship crew.

2. The Dungeon. Heroic Fantasy on the surface. Players are Seasoned Adventurers^TM sent on a quest that turns out to be more dangerous than any dragon or evil wizard, something that even the wisest of sages would be driven mad to comprehend.

I could run either game (or both; they're obviously different). Both would be run in a black-box home-brew system.

Technically "Existential Horror" is part of the whole Lovecraftian horror thing.

I would be interested in in the sci-fi version depending on the system you use.

Part of it, but not generally as applied to tabletop roleplaying games. I don't know that SAN does a good enough job; I'd rather have a group of players who can self-motivate their mental breakdowns rather than have it forced on them mechanically.

System is home-brew, very light, behind the scenes, ideally entirely invisible, but of a "realistic" power level. Try things that you would expect people to be able to do in real life.

A good CoC GM will usually let a good player pick (or even come up with) there own insanities.  I've usually just used SAN as a mechanic to decide when it happens, only resorting to rolls on type if the player is unsure what kind of breakdown it should be.

So you're talking more like free form RP?  Like a guided type free form?

Rules light, not free-form. Tell me what you want to do, I'll tell you what happens when you try. You control yourself, not the reactions of your fellow players or NPCs. That sort of thing.

I like the idea for the campaign.  I'm just worried about the rules.  I prefer 'crunchy' type rules, never did any 'rules-light' stuff.

There's actually a game called JAGS (Just Another Game System) with its own supplement called JAGS Wonderland (yes, based on Carrol's Alice in Wonderland). Both books are available for free (as PDFs), and I think could totally fit in with your idea. It's pretty flexible, too; can be "soft" or "crunchy", played just right. Or just use Wonderland as a setting with a different system, like GURPS.

Just search the interwebz for JAGS Wonderland; you'll find them.

I'd love to play if you went with that, as long as you use a free system (can't exactly gamebook shop right now), or something easy to pick up. I've wanted to play that setting for SO LONG.