GroupOffice is a groupware suite that takes your office online, implementing online collaboration and CRM. It allows you to share projects, calendars, files and email online with co-workers and clients. It is easy to use and fully customizable. It also features synchronization with PDAs and Outlook.
The Apache Open For Business Project is an enterprise automation software project that includes ERP, CRM, E-Business/E-Commerce, SCM, MRP, and CMMS/EAM functions. It is a foundation and starting point for enterprise solutions and can certainly be used out of the box, but is also great for creating specialized applications.
Drivel is a GNOME client for working with online journals, also known as weblogs or simply blogs. It retains a simple and elegant design while providing many powerful features, including support for LiveJournal, Blogger, MovableType, Advogato, and Atom journals. (Systems based off these are also supported, including WordPress and Drupal.)