Mailmeteor - Send hundreds of personalized emails with Gmail.
HEY - Email at its best, new from Basecamp.
GMass - GMass allows you to easily schedule emails, send out mass emails and mail merge campaigns and more with Gmail! Click here to learn about more features!
Horde - Horde Groupware is a free, enterprise ready, browser based collaboration suite.
Email on Acid - We make the send button safer. For every campaign, every message, and every inbox, Email on Acid has the time-saving tools you need to put your best email forward.
InstAddr - Disposable email address application.