Yakuman is a 1989 mahjong video game developed by Intelligent Systems and published by Nintendo for its handheld Game Boy system.
One of the four original Game Boy games available for the Japanese launch of that system on April 21, 1989. Released alongside Alleyway, Super Mario Land, and Baseball, it bears the distinction of being the only of the four Japanese Game Boy launch titles never released outside of Japan.
If you have two copies, two Game Boys and a link cable, you can play two player mode. Yakuman is the name of the winning hand in the Chinese board game, mahjong.
Source: Wikipedia, "Yakuman (video game)", available under the CC-BY-SA License.