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

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

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]

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

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

A webmail client based on PHP and MySQL. Features include folders, multiple POP3 / IMAP accounts, address book, calendar, modular design to add new functions. It's multilingual and theme based. [Open Source and commercial versions]

A friendly and easy wapmail interface to use your email from mobile devices. Developed in PHP 4 for Apache or Microsoft Internet Information Server (IIS). [Freeware]