I've released a demo (Including source code and tools) for the IGS PGM Arcade system. It's available from http://arcadedev.emuvibes.com
Given that MAME emulates some of the games on this system, he could have pulled the info from there...
MAME, and tracing through the debugger. The hardest part was making sense of the graphics format. Finding the entry point into the code wasn't as hard as the Neo Geo MVS.
I *finally* got around to releasing my Frog Feast port for the IGS PGM, in addition to the source code and tools. They are located at http://www.rastersoft.net/FrogFeast/ This is pretty close to a complete game (minus handling coins/credits), and most of the game logic is in C. The C game code is shared between many different systems. Only the setup and routines are specific to the system.