From an end-user perspective there doesn't appear to be much difference between this module and the AmazonS3 module, is this duplication of effort? If so, is there a good reason for it?
It's obvious from the project page that there are some technical differences between the modules:
Special recognition goes to justafish, author of the AmazonS3 module. S3 File System started as a fork of her great module, but has evolved enormously since then, becoming a very different beast. The main benefit of using S3 File System over AmazonS3 is performance, especially for image-related operations.
But it's not clear whether an attempt was made to contribute these improvements to the AmazonS3 module or whether they were rejected (necessitating a fork). S3 File System being a 'very different beast' isn't a particularly satisfying answer, since ‒ with a bit of collaboration ‒ the two codebases could still be merged, and it's mostly irrelevant to users how the module is implemented (just that it solves their problem).
Some problems with duplication of effort are:
I apologise if this has already been discussed somewhere, but I couldn't find any issues. Please could you find a way to work together with justafish on creating one great module, instead of two good ones?
Closed: outdated
2.0
Miscellaneous
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
Drupal 7 end-of-life triage:
Drupal 7 reached end of life on January 5th.
The 7.x branches of S3FS do not have any additional planned releases.
The AmazonS3 module has not released a new version since 2015 and does not have a D8 release.
It does not appear there is any remaining duplication of effort to be avoided as it relates to the AmazonS3 module.