Hastymail is a free IMAP webmail software (open source) built with PHP.

The application is lightweight, has a clean interface & compatible with all major browsers including mobile ones.

Free Webmail Software

With its plugin support, new features can be added. Some available plugins are: calendar, filtering, RSS/Atom.

Hastymail can be customized via CSS & has a PHP based template system.

It has Vcard based contact list with multiple import/export ability & many other features.

WebResourcesDepot Feed