AfterLogic WebMail Pro PHP

Webmail front-end for your existing mail server, written in PHP (source code included). Provides fast and easy-to-use AJAX interface, supports POP3/IMAP/SMTP/SSL, folders, private/shared/public calendar, rich-text editor, address book (contacts and groups), message preview pane, many accounts per user, filters, web admin panel, non-English languages, skins, UTF-8. Database supported: MS SQL/MySQL. Easy install. Free 30-day trial
Atmail

@Mail is the complete WebMail solution for your site. Utilize mail resources via a feature rich web interface or Wireless devices. Features include: POP3/IMAP support, attractive WebMail interface, Mozilla XUL interface, personal and group-scheduler/task utility, Groupware Sync support for Outlook, personal and group address-book, user preferences, multiple accounts, migration scripts, Email to SMS support, 100% customizable interface, in-depth Web-based administration of accounts. Large Selection of multi-lingual interfaces available. Compatible with most Unix and Windows platforms. Online and download demo available.
gwebmail – high performance webmail

Gwebmail is high performance php/mysql webmail on top of an IMAP server, it will extract and display your messages in a nice full featured, ajax powered interface
