ceph - http://docs.ceph.com/docs/master/radosgw/s3/
swift - https://wiki.openstack.org/wiki/Swift/APIFeatureComparison#A...
manta - https://www.joyent.com/manta
SWIFT is indeed analogous to S3.
Unfortunately, Basho has been so successful with their TSDB and KV products that they have basically put S2 on maintenance mode. They are still "supporting" it, but no new features. I was hoping this Minio tool could do something similar, but with a single daemon is a single point of failure. Unacceptable for serious deployments.
http://www.slideshare.net/rakutentech/scaling-and-high-perfo...
Everyone's got their s3 of choice, always good to have more options on the table.