Idea: Provide a world for users to fill with secrets.

Just an open brainstorm as to how you might implement this. For a tabletop RPG, it seems like you could use a wiki-like approach to build a campaign setting full of intrigue and hidden motives; the person handling the meat of the setting serves as the admin, with others stepping up to suggest various motives/intentions/goings-on for everything from shopkeeps to nobles to the beggars in a given alley. The big design question is how you'd handle this in some kind of video game.

The approach I'd envision there is making a moderately expansive 3D world, with several different wilderness environments, some small and large towns, etc. It'd hopefully be done well enough that it'd be moderately interesting and beautiful, something you might enjoy running around in with no particular direction; at the same time, it'd all be within the bounds of normality (albeit with the landscape distilled a little, so that you've got more fancy waterfalls and so on). But you'd also provide a set of tools that users could use to modify or add to the world, providing various assets but also letting you make your own.

I can open up this toolset, go in, and add something like a small grove in the middle of a forest or a strange rock formation. I can also go much further than that, adding things like a hidden valley containing ancient ruins or an underground cave system. Other options could include things like giving a seemingly generic building a working door and an interior, and a creature creator that lets you give them all kinds of different behaviors (i.e. your little stick-man will always stay far away unless the player stands still for at least 10 seconds while the moon is full). There'd be a moderator panel I can check in with; they'd offer feedback and be the ones who'd incorporate the altered region into the world. (These moderators *could* act as quality control, but I think their main priorities would be to avoid having one user's additions conflict with another's (i.e. they'd inform you that there's already something going on with that cliff face, and suggest several similar areas to implement your idea instead) and maintain a couple of general guidelines (secrets shouldn't be obvious from a distance, though subtler clues are fine). Players should feel free to give their contributions all kind of unique quirks- winding trails of sky-blue flowers that lead to hidden cave entrances, inscriptions on walls that tell fragments of a story. . .