Other Space Operas and similar projects
Colony Ship - midsize
Image from Anders Sandberg

Worldbuilding projects on the Net, current and historical

BigIdeasGrandVision A space opera scenario written by Anders Sandberg and others in 1999, which directly inspired OA, and several of the worlds from BIGV were adapted for Orion's Arm

Beacons in the Dark - a Space Opera worldbuilding project, by OA contributor Lilly Harper

The Starmoth Universe a socialist, solarpunk world building and fiction project by Isilanka

The Epiphany of Gliese 581 by Fernando Borretti A linguist, a chemist, and a comparative psychologist explore the ruins of a dead superintelligence. (26K word story, heavily inspired by Orion's Arm.)

Vergeworlds by OA contributor Dr. Luke Campbell

Galactic Association of Intelligent Life

The Hamilton Institute of Exopaleontology (archived material) by Aaron Hamilton; another project which inspired OA, and parts of which were adapted for the Orion's Arm scenario

Ad Astra by Richard Baker and D. Dye. Richard was an early contibutor to OA, and this site was another inspiration for OA.

Eclipse Phase A prominent transhumanist RPG

Mars and outer planets trading post

Transhuman Space A prominent transhumanist RPG by Steve Jackson Games, Partially written by OA contributor Anders Sandberg