The best File Copy alternative to Syncthing is FreeFileSync, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 100 alternatives to Syncthing and three of them are File Copy Utilities so hopefully you can find a suitable replacement. Other interesting File Copy Utility alternatives to Syncthing are rsync and Rclone GUI.
Open-source software for syncing and backing up files across Windows, macOS, and Linux by transferring only essential data.
UI is not as nice; some features seem to be available only after donating (so “Freemium”, not free)
Utility for Unix file and directory synchronization using delta encoding for efficient transfer, supports compression, incremental backup, remote operation via SSH, customizable filters, permission and timestamp preservation, and daemon mode on TCP 873.
rsync is a pure command line client, requiring explicitly the command to be typed, with accurate data on the destination whereas Syncthing seems to run in background. This would require to use rsync plus something else (e.g. a scheduler, cron, acron, pick one)
I like rsync as an alternative to synthing because it can do pretty much the same. I like to use rsync for one off transfers or backups and syncthing for mirror syncronization.
they have some overlapping features but are pretty different tools. rsync is much more powerful in the diversity of things it can do and is purely command line. syncthing has a web interface (in addition to cli for those who are so inclined) and device apps and is simpler to set up. rsync will easily let you hose your files if you use it wrong whereas syncthing is more set up to avoid that.
A GUI for Rclone, with additional features including batch file generation, auto cloud setup, and saved file/folder paths.
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FreeFileSync is less prone to errors. I trust it more than Syncthing.