Lightweight Open Source webmail written in PHP and JavaScript
IGSuite is a web-ajax-based Integrated Groupware Suite
Simple, modern & fast web-based email client
Jnestor is another majordomo in java
Free and open source webmail software
Go Gmailer is a java based desktop app to send emails.
A winform application in C# sends files to mailbox for backup use.
Sending mail with your Gmail Account with out any Web browser support
Email client for sending emails to someone using any chosen Name
Newsletters / emailing Tool