Dropbox - Online Sync and File Sharing
OwnDrive - OwnDrive is a web-based storage platform allowing the professionals, enterprises, and individuals to easily upload, store, backup, share and collaborate on their files and data with others.
Box - Box offers secure content management and collaboration for individuals, teams and businesses, enabling secure file sharing and access to your files online.
Google Cloud Filestore - Fully-managed cloud file storage
Google Drive - Access and sync your files anywhere
Librevault - Open source zero-knowledge peer-2-peer file sync designed with privacy in mind.