The Kolab Groupware Solution offers flexible Personal Information Management (PIM) for professional deployments in companies of almost any size. But since it is Free Software, it can also be used by individual users who care about being in control of their personal information.
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.