The author is also not really clear on what they are actually needing.

If they just want webfile interface then a webserver with simple auth and webDAV would work more than well enough.

The problem is that they then go onto talk about lots of projects that all have posix interfaces. Which is slap bang into shared filesystem land.

S3 is not a filesystem, and nothing shows that more than when you use it as an object store _for_ a filesystem.

Depending on the access requirements, if you're doing local to local, then NFSv4 is probably more than enough. Unless you care about file locking (unlucky, you're in shit now)