The setup is several laptops (Linux and Mac OS) which need a shared folder but do not have consistent access to the network. The files would need to be useable while offline and any changes be uploaded and downloaded upon reconnection with no interaction needed unless there is a change conflict.
Possible solutions reviewed:
Git - requires regular interaction and not intended for large binary files
Rysnc - only one way and does not handle merging changes
Samba/nfs - They don't keep a local copy and manual copying eventually becomes a huge merge issue