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
Nextcloud - With Nextcloud enterprises host their own secure cloud solution for storage, collaboration & communication from any device, anywhere.
FreeFileSync - FreeFileSync is a free open source data backup software that helps you synchronize files and folders on Windows, Linux and macOS.