I am getting more and more bummed that I sold off those games at Kubla!
So with Microscope, is the world-building the whole point? Or is it like a first-session thing? Either way it sounds cool. Another RPG with a shared world-building component is Burning Empires (which I sold!) which is a conversion of Burning Wheel (which I sold!). It's set in some comic-book scifi universe and is themed around alien invasion. It's set up as an oppositional (GM vs players) campaign of fixed length, about 8 sessions if I remember right. Anyway, you spend the whole first session "burning" the world the campaign takes place on along with the PCs and the most important individuals in the campaign. I never got far enough in the rulebook to really get a good bead on the rest.
Burning Wheel is probably WAY too crunchy for our group (heavy rules, basically requiring buy-in from everyone in the group) but it's fun to browse through. Although it is not set up with worldbuilding or as an oppositional game like Burning Empires. It's also sort of default Tolkien-fantasy themed.
Another RPG I've been getting a little interested in is The One Ring. enr0n and I played this at Kubla in 2012 and even with a not-so-stellar GM, it was lots of fun and a very interesting system. Basically it's set in the time around the Hobbit, focusing on the Mirkwood area, and has lots of interesting flavorful mechanics built in around traveling, companionship and so on. Like anytime you travel there's a whole little minigame you play. Anyway, they just came out with a revision edition PDF and the hardback releases later that year, I may pick it up when it comes out (and then sell it to you for cheap at Kubla in 6 years).