Jim Henson spent many hours at the Robotorium, INC with Debbie the Roboteer learning to use the new Apple IIE desktop computer (her cousin programmed with the first RS232 interface ports) and interfaced with a Rhino XRII bored out airplane aluminum 6 to 8 axis robotic arm. Through experimentation they came up with a way to have one puppeteer use an actuated mitt controller arm to animate miniature puppets (the worm-like critters) or even choruses of different puppets through the use of the same robotic applications and programming. The mitt ran the motors on each axis of each of the puppets. The puppeteer put their arm into the mitt controller and went through the motions.
The names "Gobo" and "Traveling Mat" are film-industry in-jokes. Gobos are used to control the shape of light emitted from a source and traveling mattes are used to combine two or more image elements into one final image.
The Doozers represent the working class, the Gorgs represent royalty/nobility/idle rich. The Fraggles represent those in the middle, who work a bit, but not as much as the doozers, and seem to live off their constructions.