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.
ADJE WebMail is a set of Perl CGI scripts which provide a Web interface to existing email accounts on any POP3-compliant email server. The software provides a complete interface, including encoding/decoding attachments, email and URL markup in received emails, and an address book for each user.
OpenPSA is a Web application designed specifically to meet the needs of Web agencies and consultants. It aims to be a one-stop solution for the management of typical agency business processes, such as project management and time tracking, invoicing and document management, and group calendars. It also includes CRM features such as sales force automation and direct marketing, and is extendable via the builtin component framework.