Fire Emblem 64
Credits: Shu, Serenes Forest
Fire Emblem 64 was a Fire Emblem game that was supposed to be released on the Nintendo 64, and would have been the 6th game in the series had it been released. The game was also supposed to be a disc for the 64DD, which was also not released. Miyamoto stated that a Fire Emblem game for the 64, if ever made, would come out after the release of Super Mario RPG 2, which was also never released.
Though Nintendo supposedly talked about FE64 off and on in the late 90’s, it became known as a cancelled project on September 22nd, 2000.
Based on the few screenshots of a prototype version of FE9 floating around the internet, it is speculated that FE64 may have led to Path of Radiance, but there isn't much information to base this off of. In a 1996 interview with Fire Emblem creator Shouzou Kaga, it was stated that he wanted to continue Marth’s adventures on Akaneia.
This interview and other pieces of info can be found here.
Fire Emblem 64 is an interesting piece of Fire Emblem history, and though we probably won’t find out much more about it than the little bits of information that has been gathered thus far, fans can still speculate and wonder about this long lost Nintendo project.