IlohaMail is a lightweight, multilingual Webmail client that is easy to use and install. It runs on a stock build of PHP, and does not require databases (although database support is available) or the IMAP library (it is powered by a custom IMAP/POP3 library). It also includes basic PIM-like features, including a calendar/scheduler, a full fledged contacts manager, and a bookmarks manager.
Webtop is a Web-based POP3 email client that includes SSL encryption, Mozilla support, many email filter options, spam fighting features, custom folders, email import/export, fast searching, undeliverable email bounce, intelligent read receipts, and email-to-PDF generation. The Webtop also includes a calendar, notepad, online file storage, automated email reminders, contacts, mailing lists, and Web-based administration. One installation can support multiple users and each user can set up as many POP3 accounts as they need.
OfflineIMAP is a tool to simplify email reading. It allows you to read the same mailbox from multiple computers and ensures that your changes will be automatically reflected on all computers. You can use various mail clients to read a single box or read mail while offline with full synchronization when you reconnect. You can read IMAP mail with readers that lack IMAP support (same goes for SSL). OfflineIMAP's multithreaded synchronization algorithm performs between 10 and 60 times faster than many mail readers' internal IMAP support, and it can be used even with mail readers that support IMAP already. There are five available user interface modules, including scripted execution, an interactive terminal interface, and GUI interfaces.
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.
Diom Webmail is a Web mail client written in PHP to interact with an IMAP server. It is easily configurable, with common features like sending and receiving messages and attachments, an address book, user configuration, and a spell check. It makes full use of MIME headers, and allows users to read and send messages with MIME content, like attachments and HTML messages. The look of Diom Webmail is easily customizable using a global CSS file. Configuration is run by a MySQL backend.