Fisy is a bidirectional file synchronizer for multiple hosts sharing a single server. It can be used as a "private cloud" while allowing you to work offline. It is useful for backups where you also want the benefit of being able to access the files directly on the server.
The server-side storage uses flat files, so inspecting the state of a backup can be done with normal file tools. Hardlinks are used to deduplicate data. Uploads are copy-on-write. Collisions between multiple hosts are handled at download time (or through a web interface). I.e. uploads will still succeed, and there is no ambiguity of where a file came from.
Don't use this software for data you care about. It has seen very little testing.
Distributed under the MIT License.