Dropbox - Online Sync and File Sharing
Syncthing - Syncthing replaces proprietary sync and cloud services with something open, trustworthy and...
ownCloud - ownCloud is an open source project enabling businesses to host their own cloud storage while maintaining regulatory and compliance needs.
Google Drive - Access and sync your files anywhere
Mega - Secure File Storage and collaboration
Nextcloud - With Nextcloud enterprises host their own secure cloud solution for storage, collaboration & communication from any device, anywhere.