SquawkGear
SquawkGear allows you to fly FlightGear on VATSIM, using a couple of old VATSIM clients, SquawkBox 747 and Advanced Voice Client.
What is VATSIM?
The <a href=http://vatsim.net>Virtual Air Traffic Simulation network</a>. "VATSIM is an online community where people can learn and, at the same time, enjoy the pastimes of flight simulation and air traffic control simulation all while making new friends from all over the world." http://www.vatsim.net/vatsim/
History
Curt thinks it worth pushing towards VATSIM connectivity "a bridge... acts as a FG multiplayer server..." - Curt http://www.mail-archive.com/flightgear-devel@lists.sourceforge.net/msg20971.html
"FG users stand to benefit" - Curt http://www.mail-archive.com/flightgear-devel@lists.sourceforge.net/msg12538.html
Similar concept in 2006 (XPlane - FG) http://www.mail-archive.com/flightgear-devel@lists.sourceforge.net/msg03730.html
From FG forums: http://flightgear.org/forums/viewtopic.php?f=6&t=533 and more specifically: http://flightgear.org/forums/viewtopic.php?f=6&t=533&start=60#p66399
Concerning multiplayer (visualisation of network air traffic): http://forums.vatsim.net/viewtopic.php?f=8&t=47884
Concerning the NDA: http://forums.vatsim.net/viewtopic.php?p=350103#p350103 and http://forums.vatsim.net/viewtopic.php?p=350127#p350127