Part of the "Megastructures: The Visual Encyclopedia" book project, on sale now at http://www.neilblevins.com/projects/megastructures/megastructures.htm
A Rungworld is an orbital structure that links together several hundred McKendree Cylinders into a ring that resembles a bent ladder. The ring could float in space, surround a planet, or have a star at its centroid.
Unlike the Ringworld, spinning the entire structure for gravity wouldn't be necessary as each individual cylinder is spinning around its own axis to provide spin gravity to the cylinder's inhabitants. Cylinders could be added or removed from the overall ring as needed, the remaining cylinders would adjust their spacing to compensate.
Each cylinder could be a nation state, with wildly differing landscape and climate, even differing atmosphere if alien races were included. Fleets of spacecraft would travel between and trade goods with neighboring cylinders.