UebiMiau is a simple, yet efficient cross-plataform POP3/IMAP mail reader written in PHP. It's have some many features, such as: Folders, View and Send Attachments, Preferences, Search, Quota Limit, etc.
Usermin For Webmail
Usermin For Webmail is a modified version of the Usermin package that is pre-configured for use as a Web-based email client. It is designed to work on systems running a local IMAP server, such as Dovecot. By default, users can read email, setup autoresponders and forwarding with Procmail, filter mail with simple rules, change their passwords, and manage folders.
W3Mail is a fast and small web-mail client written in PHP5. It provides easy webmail access to IMAP accounts and has very few requirements to install. Features multi-language support, simple contacts manager, MIME attachments, displays HTML messages. W3MAIL supports leading open-source database engines, PostgreSQL and MySQL. Translations: English, Russian.
WAPMail enables users to view their e-mail from any IMAP enabled server.
Fully Customisable web interface for email servers allowing web access to email from anywhere.
WebMail is a simple set of PERL scripts, it works using module Mail::POP3Client, and allows to send and receive mails.
werkmail is a browser-based mail client handling imap and pop3 mail servers. it supports attachments (viewing and sending), carbon copies, blind carbon copies, forwarding messages, replying.
WizMail is a webmail system, featuring a nice design, filters, a client to access your mail server through an HTTP proxy, etc.