This open source Roam Research clone is now open use:

https://twitter.com/AthensResearch/status/1364380119763013636

It is still very basic though. For instance, no Roam import yet. A lot of people say that for Roam Clones, Logseq is much further ahead:

https://logseq.com/

Meanwhile, work seems to be moving ahead on the Roam API and the developer has said a mobile app is a high priority, with something coming out this year, maybe even sooner rather than later.

Athens is starting to shape up nicely. The free tier must be self-hosted, and as a Roam clone the User tier is a comparatively-reasonable $72/yr. Nice overview video here

https://www.loom.com/share/ee5120d1f69d4ce0aab923de71caedd0

and they also have a Discord (who doesn't these days?)

https://discord.com/invite/PFJzpbz

Have not explored this much, but I know a number of people really like Dendron as well https://wiki.dendron.so/