Never seen one so what does it do?

Tests CPU Switch Matrix, Lamp Matrix and all coils(cpu controlled and special).
Uses a small LCD screen to replicate the score display, so you can run all the standard diagnostics from the board and view results on the mini screen.
Runs on +5v and +12/-12v, so eliminates need for high voltages for displays. Built in DVM and logic probe with display on the LCD.
Can be used with Williams system 3 - 11 CPU boards.
Lots more info on the website.