The author seems to be violating the GPL with Menuet64? Menuet64 is pretty clearly a derivative work of Menuet32, which is GPL. However, Menuet64 is released under a non-free license.
Originally I believed the author may be the sole author of Menuet32, and thus could relicense to whatever they wanted. However, the release notes (https://www.menuetos.net/relnotes.htm) credit many other authors with their contributions.
No, M64 was never free, as far as I can tell. I remember stumbling over M32 around 2006, when I was interested in OS development while being a CS student. I kept interest, and some time later a 64 bit version was published, but no source code, unfortunately.
The project kept growing a bit, very slowly. Seems like after v1.00 the author lost most interest. So if it is still a prototype work without any commercial usage, it would be great to have it published with source code.
Originally I believed the author may be the sole author of Menuet32, and thus could relicense to whatever they wanted. However, the release notes (https://www.menuetos.net/relnotes.htm) credit many other authors with their contributions.