We make distributal software that stores some data (attachments) in a) a database or b) Amazon S3. The database is used because it requires no other configuration. Amazon S3 is the better option.
What we want now is a solution for customers that don't want to use Amazon S3. We can obviously just use the filesystem but this can be problematic if there are multiple web servers and the files need to be replicated; it also requires us to write extra code to handle the various permuations of problems that can happen.
What we would prefere is if there was a piece of server software that essentially replicates Amazon S3's API. That way our clients can install the server on a box; and we don't need to change any code. So ... is there any such software out there?