Unraid provides real time data protection, whereas Snapraid with mergerfs provide disk pooling and scheduled snapshots. That's its greatest feature IMO - expandability and data protection without rigid expansion requirements.

AFAIK, it's one of a kind. Flexraid on Windows was the closest I had found (a product I still use on an old install - software and owner disappeared - although I did manage to track down the patent and the developer once, seems to have moved on to other interests/employment)