Chandler is an open source Note-to-Self Organizer designed for personal use and small-group collaboration. Chandler consists of a cross-platform, desktop application, sharing service and web application.
Citadel is a turnkey open-source solution for email and collaboration. One simple installation delivers a multitude of powerful features, including: email, calendaring/scheduling, address books, bulletin boards, mailing list server, instant messaging, multiple domain support, modern AJAX-style web interface