HTTrack - HTTrack is a free (GPL, libre/free software) and easy-to-use offline browser utility.
iRedMail - A fully fledged, free email server solution, an open source project (GPL v2).
WebCopy - Cyotek WebCopy is a free tool for copying full or partial websites locally onto your harddisk for offline viewing.
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.
SiteSucker - SiteSucker is a Macintosh application that automatically downloads Web sites from the Internet.
mailcow - An open source mailserver suite.