The 27 planets stolen by Davros and the Daleks in the Doctor Who Episodes "The Stolen Earth/Journey's End".
How about this for a science fantasy campaign, inspired by the 4th season of Doctor Who, Spelljammer, and the Savage Worlds setting Slipstream:
A cosmic being steals random worlds from across the Multiverse for an unknown purpose. The being places the planets in a pocket dimension bordered by various dimensions. The worlds orbit each other in a complex pattern, and the dimension seems to light and darken to give the impressions of day and night. With that, the cosmic being disappears.
After the initial chaos of the Stealing, the denizens of the various planet go out to meet each other. Alliances are made, battles are fought, and conspiracies are begun. World that have not contacted the other planets are marked for exploration. Travel between the planets is made possible by ships powered by science, magic, psionics, and other motive forces. And the greatest question of all is the mystery of why the planets were taken in the first place.
Take a bunch of worlds you always wanted to have interact with each other and throw them in the mix. May do something with this in the future...