TDEV was made by SN Systems and sports a custom mainboard with 48MB of 1T-SRAM which is double the main RAM a GameCube has. It also uses a custom USB 2.0 speed module from Serial Port 2 which games are simulated on. The extra RAM may have likely been added to cache files from the USB connection and to host in-game development tools that would require extra memory. The console runs a custom IPL as seen in the pictures linked below. It can boot NR discs only, and only came in a brown colour.
The PC side software is SN SYSTEMS PRODG and requires a valid license to run.
http://www.gc-forever.com/tdev for pictures of the internals.