I’ve wanted to do this but never have. Have you done it?
The idea is simple, the execution complex. For each major chapter in your RPG campaign, you use a different game to resolve the action. You hack and modify the games you want to use like crazy, some more than others. What starts as an investigation lead by various governments in a weary, war-torn metropolis leads to the highest tier of society (Cold City). There, in glorious and lavish penthouse ballrooms untouched by the war below, the glitterati dance and drink and dare each other (via The Dance and the Dawn) to determine who gets whom. That leads to a Fiasco involving miserable spouses, true love, stolen diamonds, and broken hearts that return us to the lowest levels of the city.
Or what about a military campaign that plays out over a century, beginning with complex machinations and paranoia (via Burning Empires) before progressing to the madness of an all-consuming galaxy-wide war (via 3:16 Carnage Amongst The Stars) and finally culminating in the least likely soldiers fighting in the bombed-out remains of the last human city (via Grey Ranks).
A great many of these games don’t let many characters out intact, so the traditional notion of following a core cast of PCs on a long literal or figurative journey might not work out. Rather, it might be necessary to tie individual games together with a few standout characters—who are playable only in certain chapters, maybe—or narrative connective tissue like monologues, flashbacks, or just a recurring theme or motif that brings together what would otherwise be a loose anthology.
My gut says this idea would require a lot of cooperation, maybe to the point of demanding certain metagaming choices be made during play, but I think the unique satisfaction from pulling it off would be worth it for the group that finds this compelling. Remember, the game that covers the next chapter wouldn’t have to be preordained. It might be that whoever gets the happiest result of the Fiasco story gets to decide what the next chapter is about, for example, so this wouldn’t have to be a strictly planned experience.
What games might you connect into a campaign if you could?