PHP system that allows one to offer personal email accounts to the site visitors. Complete customization, attachments support, and spam filters. [Commercial]

A light-weight multilingual webmail client with POP3 and IMAP support, written in pure PHP4. [GPL]

Very popular IMAP webmail program. It relies on PHP3's IMAP module for the IMAP calls, and an SSL server for security. [GPL]

Just Another Web mail is a flexible, powerful and fast webmail written in PHP [GPL].

A web-based client to check your POP3-mail.

IMAP based webmail client for PHP.

A webmail system based on PHP and MySQL, designed for small-to-large web sites and enterprises [commercial].

A standards-based webmail package written in PHP4. 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) for maximum compatibility across browsers. [Free]

An IMAP Client written in PHP3, with support for calendar, notes, much more, and support for extra plug-ins. [GPL]