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Haiku has been ported to RISC-V: https://www.haiku-os.org/blog/kallisti5/2021-11-07_booting_our_risc-v_images/

Hubris

There is an initial port of Hubris to the Freedom E310 core on a Sparkfun RED-V board: https://github.com/oxidecomputer/hubris/discussions/365

 Note from Cliff:

> In general, Hubris was originally designed with the intent of moving to RISC-V eventually, which is part of why we're so register-focused in the calling convention.

Illumos

Illumos has been ported to the Allwinner D1: https://github.com/n-hys/illumos-gate/wiki/Allwinner-D1-Nezha

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