https://www.minio.io/
https://www.openstack.org/software/releases/ocata/components...
If you're serving a static site out of S3, put Cloudflare (ugh) in front of it and enable the feature to serve your cached content when the origin is down [1]. When S3 goes sideways, as everyone is learning, it goes down hard and you're probably not going to be able to make changes to objects, read object metadata, etc.
[1] https://support.cloudflare.com/hc/en-us/articles/200172256-H...