There is OmniOS[1] as well, fits next to OpenIndiana.

https://omnios.org.

Open Maryland, Not Indiana :) (So named in this case because the company that released it, OmniTI, is based in Maryland. Source: worked there at the time) It's a good OS, as I imagine the other Illumos derivatives are, but sometimes the relatively small size of the community can be felt, e.g. in breadth/depth of available third party packages and update availability/timelines.