[@CornixElecti] often enough, you can stumble upon an original RP which will be entirely made up, though there are a good deal of GMs who will create fandom-based RPs simply so that there is less work for them to have to do (as someone who is currently in the works of crafting an [i]entire world[/i], I can definitely understand why they would go that route ._. making lore is rather time-consuming!)

Let this not discourage you, though! There are definitely some really great, original RPs out there that are being crafted, and be sure to check both the main Roleplay forums as well as the Interest Check forums for RPs either still being created or just starting! It may take a bit of perusing, but there are certainly some in there that could perhaps be to your liking. Casual is perhaps better suited for having a deal more original RPs (and more RPs, overall), though I do think that there are still a few in Free that aren't entirely based on any sort of fandom. Like I said before, it just takes a bit of patience and sorting through the first few pages before you can land on one that really draws your attention. And, if it comes to the point where you don't find an RP that really sticks, feel free to tackle the task of creating an original RP all on your own!

EDIT: Just as a precaution, here are the links for you:

[url=http://www.roleplayerguild.com/forums/3-free-roleplay]Free Roleplay[/url] - [url=http://www.roleplayerguild.com/forums/12-free-interest-checks]Free Interest Checks[/url]
[url=http://www.roleplayerguild.com/forums/4-casual-roleplay]Casual Roleplay[/url] - [url=http://www.roleplayerguild.com/forums/13-casual-interest-checks]Casual Interest Checks[/url]