Kart Fighter Improvement is likely a ROM hack or a modified version of the original Kart Fighter (Unl) NES game. As a modification, details about the original developers are unavailable. The 'Improvement' suggests enhancements or changes to the original gameplay or graphics, such as improved balance, bug fixes, or added content. Without access to the ROM, specifics on the changes are unknown. 

Kart Fighter Improvement

Karnov (Japan) [En by Vice v1.1]