A seller on GameGavel has listed a few prototype arcade boards.
First is a board sent to Romstar for game testing to see if the seller would license and sell Ghosts & Goblins.
Then you have aÂ Kageki Prototype. The original Kageki was built up on a Revenge of Doh main board with a perf boarded speech synthesizer section and strapping for 1 meg graphics chips. Theboard for sale was used to test on location for earning capabilities to decide to market Kageki. A new board was designed for the production run.
Last, there is aÂ Prototype Pipi & Bibis. This was a testing board with graphics roms on sub-board.
They also have aÂ Kyle Hodges game, VR8. Virtual Combat. Apparently a super rare game board.