NeoMail!

Roundcube webmail is a browser-based multilingual IMAP client with an application-like user interface. It provides full functionality you expect from an e-mail client, including MIME support, address book, folder manipulation, message searching and spell checking. Roundcube's most prominent feature is the pervasive use of Ajax technology.

Apple Mail changes the way you interact with your email every day.

Polymail is the modern email client, redesigned.

SquirrelMail is a standards-based webmail package written in PHP. 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 required) for maximum compatibility across browsers. It has very few requirements and is very easy to configure and install. SquirrelMail has all the functionality you would want from an email client, including strong MIME support, address books, and folder manipulation.

MailMate is an IMAP e-mail client for Mac featuring extensive keyboard control, Markdown supported email composition, advanced search conditions and drill-down search links, equally advanced smart mailboxes, automatic signature handling, cryptographic encryption/signing (OpenPGP and S/MIME), tagging, multiple notification methods, alternative message viewer layouts including a widescreen layout, and much more.

NaSMail is a standards-based webmail package written in PHP. It includes built-in pure PHP support for the IMAP and SMTP protocols, and all pages render in HTML 4.01 with minimal JavaScript and CSS. It has very few requirements and is very easy to configure and install. NaSMail has all the functionality you would want from an email client, including strong MIME support, address books, and folder manipulation.

Atmail webmail system offers a webmail client, email server platform and mailserver appliance for Linux, Unix and Windows.

Simple Mail is a mail client for Firefox. It allows you to get notified, read and write messages for multiple email accounts inside Firefox.

GyazMail is a email client software for Mac OS X, based on Cocoa framework, simple, easy-to-use with many features.

NOCC is a webmail client written in PHP. It provides webmail access to IMAP and POP3 accounts.

phlyMail is an advanced webmail and groupware solution featuring unlimited profiles, multiple users, a calendar, contacts list and much more

Postaci (Turkish for Postman) is multiplatform Webmail software which is database independent, multilanguage, POP3/IMAP, and fully MIME-compatible. While using POP3 mode to fetch messages it uses database fields to simulate IMAP folders, on which you can save, move, delete, and read e-mail. It also contains an adressbook, a notebook, and a bookmark manager application.