Zimbra offers Open Source email server software and shared calendar for Linux and the Mac. Email and Groupware - easy to install, easy to use. - Citadel.org. CPS: an advanced and full-featured Open Source ECM framework. Last modified: 12/08/2010 08:31 AM CPS (for Collaborative Portal Server) is a complete Free / Libre / Open Source platform available for building Enterprise Content Management (ECM) applications.
CPS comes also as a user-friendly accessible application ready to for entreprise-grade content management with many collaboration features. Kolab Groupware. OpenGroupware.org. Phpgroupware.org.