They mean proprietary in the sense of "we built one ourselves". You can download source from the links at the bottom of the page: http://www.returninfinity.com/pure64.html
The distribution zip actually just contains binary pure64.sys file and sources for their example kernels. The sources for Pure64 are not included. Also, no information on licensing is included.
They mean proprietary in the sense of "we built one ourselves". You can download source from the links at the bottom of the page: http://www.returninfinity.com/pure64.html