Extinct ai culture in the Gliese 229 system. Apparently seeded from isolationistic ais which escaped from the solar system sometime in the 5th century, and arrived here in approximately 700AT.
The ais employed replicators to convert the surface of Gliese 229Ab 1 (the moon known as "Tessera") into energy collectors and computronium. At some point their society crashed, and disassemblers eroded most of the installations. Only fragmentary information remains, hinting that the collapse was not due to any outside threat or violent conflict.
This system became part of the First Federation in 1188. Even in the Current era parts of Tessera still retain the original computronium surface structures, which have become tourist destinations.