My Williams multi-game circuit board. I designed this back in 1999 before multi-game kits became popular. Much of it is based on the multi-game work done by Sean Riddle. It plays:

It has an integrated rom switcher & NVRam. I cycle through the games with the player 1 button and select the game with player 2. The original control panel is for Defender & Stargate. The 2 joystick panel is for the other games and can be switched out in about a minute.

Here's the design files (Except for the control panel mux which was just drawn on paper and built on breadboard.)