Dropbox - Online Sync and File Sharing
Box - Box offers secure content management and collaboration for individuals, teams and businesses, enabling secure file sharing and access to your files online.
Google Drive - Access and sync your files anywhere
Nubo - A self-hosted file sharing application in Haskell.
Nextcloud - With Nextcloud enterprises host their own secure cloud solution for storage, collaboration & communication from any device, anywhere.
4sync - A wonderful application that links all of your computers and mobile devices together. Easiest way to back up and sync your files online. Cross platform file management in the cloud