Syncthing

A continuous file synchronisation tool that keeps folders in step across laptops, phones, NAS boxes and servers over a peer to peer protocol, with no central cloud service in the middle. It offers desktop and mobile interfaces, encrypted transport, file versioning for accidental changes, conflict copies instead of data loss and a relay for devices that cannot connect directly.

Households and small teams use it so a document edited on a desktop appears on a phone and on the office server, and folders can be shared over WebDAV or SMB.

Setting it up on your own infrastructure keeps the history of every file on your own devices, so recovery means restoring one copy rather than contacting a provider.