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.