Dropbox - Online Sync and File Sharing
iRedMail - A fully fledged, free email server solution, an open source project (GPL v2).
Google Drive - Access and sync your files anywhere
mailcow - An open source mailserver suite.
ownCloud - ownCloud is an open source project enabling businesses to host their own cloud storage while maintaining regulatory and compliance needs.
Zimbra - Zimbra is trusted by over 500 million users to increase productivity with a complete set of collaboration tools while maintaining total control over security and privacy.