Syncthing: Peer-to-Peer File Synchronization
Syncthing keeps folders identical across your devices by syncing directly between them. There is no server in the middle and no account anywhere.
The architectural difference
Dropbox and Nextcloud are hub-and-spoke: files go up to a server and back down to other devices. Syncthing is peer-to-peer: devices exchange changes directly, encrypted with TLS, using discovery servers only to find each other’s addresses. Nothing is stored on infrastructure you do not own, and there is no storage limit beyond the disks involved.
How trust works
Every device has a cryptographic ID, and two devices sync only after each has explicitly accepted the other. Folders are then shared per-device. This makes the security model easy to reason about: there is no account to compromise, and adding a device is a deliberate act on both ends.
What it is good and bad at
It excels at keeping working directories, notes, photos from a phone, and configuration in sync across machines you own. It is not a backup tool, and this catches people out: deleting a file syncs the deletion everywhere. File versioning can retain old copies, but a real backup with Restic or Borg is still required.
It is also not built for sharing with other people. There is no link sharing, no permissions model beyond device-level trust, and no web access to files. Nextcloud or Seafile cover that.
Practical notes
An always-on device, even a Raspberry Pi, acting as a permanent peer makes syncing far more reliable than relying on laptops being awake simultaneously. Conflict handling creates copies rather than silently overwriting, which is correct but means occasionally tidying conflict files.
License
Syncthing is released under the Mozilla Public License 2.0.