Pocket Mahjong is a Game Boy title released in Japan which, as the name indicates, is a variation of the classic tile-matching game Mahjong. The Nintendo Game Boy's screen limitations likely meant a simplified version of the game with perhaps fewer tiles or a modified set of rules compared to the traditional tabletop version.  Given its popularity in Japan, it's likely the game provided a portable way to enjoy this popular pastime.  Information on the developer and specific features remains elusive.

Pocket Mahjong (Japan)

Pocket Kyoro-chan (Japan)