As Cameron314 said, it's a processor in many MOTOTRBO subscribers that allows third party software to be installed that extends the functionality of the basic firmware. One of the better know uses is the now EOL Connect Plus code, (Originally a Trident product) this had it's own loader and code.
We do a number of custom solutions solutions on it for customers, including some indoor Geo Fences built around a BLE iBeacon deployment and enabling QC-II for a public service agency on Cap Max as well as crash detection for another custom that will override the Tx-inhibit feature..
Building for the board is a unique skill, requires MOTOTRBO ADP membership and building a number of of specilized jigs for debug purposes
Lastly, it is powered off, by default and has to be enabled at the channel level (Connect Plus legacy) in your base code plug.