Just collecting the campaign ideas that are festering in my brain that I don't have time to do anything about. Right now, I don't have time to run the one I already started, and it'll be awhile before I have time again. I don't want to forget these, so I'm gonna dump them here. Maybe they will inspire someone else to useful effect.
Are You Afraid of the Dark?
Kids in a modern setting (80s maybe?) exploring supernatural phenomena in urban or suburban surroundings. For general direction think Martin Millar, Buffy, Goonies, Monster Squad, Lost Boys, Super 8, Marble Hornets (IE Slenderman stuff), Halloween, Nightmare on Elm Street, Some Stephen King stuff like IT.
Blight's Grey Agents
Paranormal investigation probably, but not necessarily, some decade between 1920 and 2020. Maybe using Zak S's suggestion of CoC characters with some Night's Black Agents skills. PCs could be part of a secret government agency, freelancers, private dicks, reporters, whatever. Totally unfair low random chance at character creation to be a supernatural being yourself, maybe. Emphasis on noir and investigation and seedyness blending into the supernatural, obviously like Hellboy and BPRD, but also Hellblazer and Hellraiser and other stuff like that.
Professor Quingle's Magnificent Contraption
PCs are a collection of 1800's eccentrics using a contraption to visit strange lands and have adventures. At home it's all pip pip and what, ho! but in the lands they visit, death could be around every corner. Sorta like original series/next gen Star Trek or Dr Who, but without future tech. Sorta like Call of Cthulhu in a way. PCs only have access to tech from 1800s or the weird worlds they visit. Maybe they go see Conan, maybe they go see a totally surreal land of disembodied intelligences that shape reality to their whims. Some games would be heavy fighting, some heavy RP, some both. Tone and genre could change every game.
Fighting Pits of Kalak-Nur
In a culture that's a fantasy version or Persia and/or Rome, PCs start out as 0-level (or 2d6 system?) slaves sent into gladiator pits, and advance by surviving their fights. At first, role play is lighter, with fellow slaves and guards. If they do something spectacular in the ring, however, they might get sponsored by a noble, introducing a whole other level. Fights are generally against animals, monsters, and NPCs, but PCs may choose to PvP in ring or out. The ring will be adorned with tactically useful terrain and weapons may be won through sponsorship.
Freedom can be won through amassing respect and money from winning fights, or through a well-executed escape plan. PCs may FlailSnail only after freedom is won. Existing FlailSnail PCs may sponsor pit fighters within reason and engage politically/financially, but may not enter the ring (or risk becoming a pit fighter at the lowest level). Pit fighters do not have to be Fighters, but may be of any race or class suitable for old school games. By the time freedom is won, PCs should have gained rumors, enemies, and allegiances such that they will enter the adventuring life with plenty to do.
The progression should be obvious here: the first several games will be really light RP and tactically interesting fights, but RP and setting stuff should grow pretty organically to become more important.
Race/Classes I'm thinking of: any basic, any random from Zak S's or other blogs, generally non-techy classes from blogs or whatever, and from Kalak-Nur - Bug People, Droids, Fire Lizards, and Blood Druids.
Certain races will be considered lower by the culture, and thus certain things will be harder at first but being "exceptional" could lead to great prestige and maybe slightly change cultural attitudes.
Yes, this setting would have slavery, explicit social strata, and casual racism, but it is a fiction and should not be interpreted to support any of that shit in real life.
Fighting Pits of the Gigastructure
As above, but in a Sci-Fi setting. Similar to Gigacrawler or taking some of what's fun about Murdermaze but making PvP optional. The above would have more mythical and real beast opponents, this would have more robots/aliens/sci fi type opponents.