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
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 Mars and outer planets trading post Transhuman Space