Dunno what systems are made for the device, but checking a list of included emulators in a so called “Onion” operating system, I see a few other devices being listed, so if you don’t mind, here are some more:

• For arcade: the other Metal Slug games up to 4 (have yet to play further), The King of Fighters 2002
• For MS-DOS: MegaRace
• For PC-98: コテ・DE・メクール
• For NES: Böbl, Micro Mages, Nix: The Paradox Relic
• For Genesis/Mega Drive: Wonder Boy in Monster World, Tanglewood
• For NDS: Shantae: Risky’s Revenge

Avoided all plot-heavy titles, even when they may have long sections low on plot.