The comments already mention several alternatives (Minio, Ceph, GarageFS). I think another one, not mentioned yet, is JuiceFS [1]. Found one comparison here [2].
JuiceFS isn't standalone, it requires separate backing storage for each of data [0] and metadata. So for example, JuiceFS would target SeaweedFS or GarageFS as its data store. JuiceFS can also target the local file system, but .. SDS use cases typically care about things like redundancy and availability of the data itself, things that JuiceFS happily delegates. JuiceFS itself can be distributed, but that's merely the control place as I understand it.
I tried JuiceFS with AWS S3 and an (admittedly slow) self-hosted postgres instance, and it didn't work at all. I would have understood if it had been really slow, but erroring it really seems wrong for software where correctness is paramount.
[0] https://juicefs.com/docs/community/reference/how_to_set_up_o...