phlyMail!

Roundcube webmail is a browser-based multilingual IMAP client with an application-like user interface. It provides full functionality you expect from an e-mail client, including MIME support, address book, folder manipulation, message searching and spell checking. Roundcube's most prominent feature is the pervasive use of Ajax technology.

SquirrelMail is a standards-based webmail package written in PHP. It includes built-in pure PHP support for the IMAP and SMTP protocols, and all pages render in pure HTML 4.0 (with no JavaScript required) for maximum compatibility across browsers. It has very few requirements and is very easy to configure and install. SquirrelMail has all the functionality you would want from an email client, including strong MIME support, address books, and folder manipulation.

A fully fledged, free email server solution, an open source project (GPL v2).

A simple, fast and secure self hosted feed and mail reader, password and bookmark manager.

Atmail webmail system offers a webmail client, email server platform and mailserver appliance for Linux, Unix and Windows.

Simple Mail is a mail client for Firefox. It allows you to get notified, read and write messages for multiple email accounts inside Firefox.

NOCC is a webmail client written in PHP. It provides webmail access to IMAP and POP3 accounts.

NeoMail is a web-based mail client that allows users to access their mail spools and send messages. It does not require a POP3 server, or any shell access for the users. It interfaces directly with user mail spools.

Postaci (Turkish for Postman) is multiplatform Webmail software which is database independent, multilanguage, POP3/IMAP, and fully MIME-compatible. While using POP3 mode to fetch messages it uses database fields to simulate IMAP folders, on which you can save, move, delete, and read e-mail. It also contains an adressbook, a notebook, and a bookmark manager application.