Snake’s Revenge is a sequel to Metal Gear that was developed specifically for the North American and European NES markets by Konami and Ultra Games. It first came out in North America in 1990, and in Europe in 1992. Why there was a two-year gap between those releases is anyone’s guess.
Hideo Koijima wasn’t involved in the making of Snake’s Revenge and it is considered ‘non-canonical’, but he did make Metal Gear 2: Solid Snake for the MSX in response to it. I’m guessing that he wasn’t particularly enamoured with the idea of another team working on his signature series, but ultimately he (rather diplomatically) says that Snake’s Revenge is “not a bad game“.