openICEM is a highly scalable server software that aims to provide a certified email service as specified by Italian law. It is based around the Postfix MTA, python-ldap, and python-clamd. It makes use of XML-RPC for communication among servers and does not require any shared service or shared filesystem.
Engroup is an enterprise groupware system promotes collaboration among members in a team or company. It also helps members manage their business better. It has the following modules: a dashboard that aggregates contents from the mail system and RSS from some known sources; private messages, an alternative method for fast communication among members to replace chatting or email; email, which supports the IMAP protocol with SSL enabled; a forum, implemented with JForum; a wiki, implemented with JSPWiki; HRM to manage employee information; CRM to manage customer information; a document management system; a project management system; a todo list to track private tasks of a user; and an RSS reader.
exJello is a JavaMail provider that connects to a Microsoft Exchange server (actually, it uses the WebDAV interface exposed by Outlook Web Access). It is designed as a drop-in replacement for the standard POP3 and SMTP providers. This allows you to send and receive messages through your Exchange server in situations where a POP3/SMTP interface is not available (through a restrictive firewall, for example, or if your administrator simply does not provide a POP3 or SMTP gateway).
WAWAS is a full PHP application server. The main server core listens to any IP/port and passes data to any mounted protocol on the listener. Implemented protocols are HTTP1.1/1.0, Comet, Telnet, DNS, mail, and FTP. Each protocol runs modules that build response data based on the requests. Memory object persistence allows data and caches to be shared across protocols or time. All configuration uses XML. It can be launched as a daemon, with or without forked workers, and is nearly as fast as Apache in preliminary tests.