Roundcube is a free and open source browser based webmail solution written in PHP with a desktop-like user interface, which is easy to install/configure. It runs on a standard LAMP server. The skins use the latest web standards such as XHTML and CSS 2. Roundcube includes other open-source libraries such as PEAR and the IMAP wrapper from IlohaMail.org.
Features of Roundcube are –
Requirements: PHP 5.2.1 or greater, IMAP Server
License: GNU GPL