Dropbox - Online Sync and File Sharing
Seafile - Seafile is a professional open source cloud storage platform for organizations.
SpiderOak - SpiderOak makes it possible for you to privately store, sync, share & access your data from everywhere.
Box - Box offers secure content management and collaboration for individuals, teams and businesses, enabling secure file sharing and access to your files online.
Nextcloud - With Nextcloud enterprises host their own secure cloud solution for storage, collaboration & communication from any device, anywhere.
Microsoft OneDrive - Secure access, sharing & file storage