Infotrope Polymer is a fully roaming online IMAP client. You can roam with your full configuration, your addressbooks, and even your bookmarks. It's fully ACAP enabled, and will operate with or without a local disk cache, and over very narrow connectivity (like GPRS), using minimal bandwidth. It supports the majority of extensions to ESMTP, IMAP, and ACAP, whether in RFC or I-D.
jwma is a Web mail implementation based on the JSP Model 2 architecture. It builds on standard Java APIs (Java Mail API, Java Server Pages, and Java Servlet API) and relies on some available open source technologies (Xerces, Castor, Jakarta-ORO). jwma is designed and implemented for use with an IMAP server. It allows complete control over the store (creating, deleting, and moving folders, mailboxes, and messages). It supports MIME messages, supports text/plain message processing (e.g. making plaintext URLs "clickable"), and supports automatic sent & read mail archiving. It features a trash mailbox, includes a small addressbook, allows simple configuration of its features, and can be used in parallel with other mail clients (like Pine or Eudora).
Hep Message Server is software that transfers messages between different messaging systems. Eventually, it should transparently route messages between email, weblogs, and instant messaging. Currently Hep does one thing: fetches news feeds from Web sites and lets you view them in your email client.