For those who haven't read it, I can only recommend +Justin Alexander
's excellent posts on game structures (http://thealexandrian.net/wordpress/15126/roleplaying-games/game-structures
As for non-dungeon and non-hexcrawl campaign frames used in OSR games, I would like to point to +Kevin Crawford
's *Suns of Gold* (trading), Skyward Steel
(military scenarios), and Darkness Visible
(espionage missions); I need to read them more than just briefly to tell if they are entirely "new", but they are a starting point, anyways.
Also, there is +John Berry
's Arcana Rising
, which has a threat-based scenario structure (although it is only described briefly, it could be developed into something more robust).
Not D&D-esque per se, but Gladiators of Legend
describes how a campaign centred around the arena and gladiators would work, while Pirates of Legend
has rules for pirating campaigns. I have only read the latter in detail, which is nicely done; I have also been thinking about porting it over to D&D (for the entirety of the rules are OGC).