What is not open source about RISC-V? As far as I can tell, there's the matter of using a trademark, and the control of the project is not given to the community.
But the specifications themselves seem free as in freedom (CC-BY-4.0):
But the specifications themselves seem free as in freedom (CC-BY-4.0):
They also have private mailing lists, but I agree, it is certainly FOSS.