Thunderbird is a total redesign of the Mozilla mail component to produce a cross-platform, stand-alone mail application using the XUL user interface language. It has many new features, among them the ability to customize your toolbars the way you want them. a new look and feel with a large number of downloadable themes which alter the appearance of the client, and the ability to add UI extensions.
EGroupware is a Web-based groupware suite. It contains many modules, including Calendar (personal calendar and group scheduling, notifications and alarms), Mail (IMAP only), InfoLog (todos, notes, and phone calls linked to contacts/CRM), Contacts (an address book for storing and sharing contact information), ProjectManager, Tracker (bug or incident tracking), TimeSheet, SyncML, CalDAV & CardDAV support, and SiteMgr content management
Exercise Tip Buddy is an easy-to-install Web site tool that allows your visitors to sign up for an exercise tip mailing list. The program comes with everything you need out of the box, including 26 exercise tips. You can easily add more tips, manage subscribers, and set the look and feel of the email so that it matches your Web site.
Tine 2.0 is a Web-based groupware solution that focuses on usability and correctness. To achieve these goals, the project uses usability experts and covers most of the code by unit tests. It contains support for contacts, tasks, calendar, email, CRM, VoIP integration, a time tracker, ActiveSync, and a flexible rights management system.
adx is a minimalistic but massively Web-enabled address book that runs completely in your Web browser. It's OS-independent and supports comprehensive details for each contact entry, including user identifiers and profiles for Skype, Twitter, Flickr, Delicious, Facebook, LinkedIn, studiVZ, instant messengers, etc. It supports the hCard and XFN microformats.