Syncthing - Syncthing replaces proprietary sync and cloud services with something open, trustworthy and...
Dropbox - Online Sync and File Sharing
Microsoft OneDrive - Secure access, sharing & file storage
Google Drive - Access and sync your files anywhere
ownCloud - ownCloud is an open source project enabling businesses to host their own cloud storage while maintaining regulatory and compliance needs.
FreeFileSync - FreeFileSync is a free open source data backup software that helps you synchronize files and folders on Windows, Linux and macOS.