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.
AODocs - AODocs is the document management solution recommended for G Suite. Secure your documents, structure your content, & automate your processes
iRedMail - A fully fledged, free email server solution, an open source project (GPL v2).
Docomotion - Docomotion offers tools for designing and generating all types of transactional and operational business documents.
Roundcube - Web-based IMAP email client
infoRouter - infoRouter is a EDMS that includes Workflow, Document routing, Electronic Forms, Scanning, Storage, Archiving, Indexing & Records Management