I implemented that in my layout, using Autohotkey scripts. After some minutes of inactivity (while in the gamelist), a random game is launched in MAME, it runs for some minutes, then quits, and another random game is launched. At any moment you can insert coin and start playing (breaking the cycle), or simply quit the running game and go back to the gamelist, which also breaks the cycle (cancelling the screensaver). This screensaver only works like that while in Mala's gamelist. If you are using Windows, he blank screensaver is used instead.