S3QL does this with sqlite. An actual external DB would give you multiple users at once, though. I've been using a combination of S3/Postgres to get filelike s

S3QL does this with sqlite. An actual external DB would give you multiple users at once, though. I've been using a combination of S3/Postgres to get filelike semantics myself, but not with a POSIX interface. The biggest problem for general use is that S3 is really for immutable file storage, and not so much things that'll change a lot. That can be worked around, obviously.