From the Traveller RPG wiki entry at wikia.com:
History of Imperium working group (HIWG) was a fan organization for Traveller.
Ed Edwards and Mike Mikesh started History of the Imperium Working Group in 1987 when MegaTraveller came out. It was originally to develop Imperial history through the Rebellion. It did a lot of this, and many ideas went into Rebellion Sourcebook and other products. It outgrew this focus, though, as people exchanged programs, wrote up sectors, and developed races.
The newsletters Tiffany Star and AAB Proceedings were published under the aegis of HIWG.