X (エックス Ekkusu) is an early three-dimensional first-person shooter-type video game software released for the Game Boy only in Japan on May 29, 1992. The game was developed by Nintendo EAD alongside Argonaut Software (who later became known for assisting Nintendo EAD in programming the original Star Fox title for the Super NES) and was published by Nintendo. X was followed by an internationally released DSiWare exclusive sequel, X-Scape. Source: Wikipedia, "X (1992 video game)", available under the CC-BY-SA License.