The best open source alternative to SyncToy is Syncthing, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 50 alternatives to SyncToy and many of them is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to SyncToy are FreeFileSync (Free, Open Source), rsync (Free, Open Source), IPFS (Free, Open Source) and Unison (Free, Open Source).
Kup is created for helping people to keep up-to-date backups of their personal files. Connecting a USB hard drive is the primary supported way to store files, but saving files to a server over a network connection is also possible for advanced users.
nsync is a free, open source software that performs synchronization of your data between desktop PCs, laptops, USB drives and more. Highlights: - Synchronize folders in 3 simple steps. - Drag & drop of folders, no complex navigation required.