Aian Ringworlds are enormous artificial rings around planets built by Aians. They usually have a habitable inside.
The shell of the Ring is made from bonded nanodiamond and aluminium and thick enough to stop both radiation and micrometeorioids that get through the repulsor shield (in the unlikely event of deactivation).
The Ringworld rotates, producing 'centripedal gravity' for those onboard. It is usually enormous, tens of thousands of miles across, so the rotation rate can be very slow.
As a settlement
Up to a billion Aians can live on a Ringworld with room for parks, leisure facilities, and ports.
In practice, it is always far less. The atmosphere and pressure are tailored for Aian needs. They are also trading posts and Aian Spaceship building yards.
As a weapon
The enormity of the Ringworld means incredibly large power sources can be built in. As such, it is known that some Ringworlds have a built in detonation device. The detonation of such a Ringworld would possess similiar energy to a supernova.
One is built around the Nightforger's prison.
Technology: Aian Ringworld, Stardeath Howitzer, Stream Cannon, Lightflame Bomb