NeverBounce - Real-time email verification and cleaning to ensure emails never bounce.
Horde - Horde Groupware is a free, enterprise ready, browser based collaboration suite.
Email List Verify - The Fastest Way to Improve Email List Deliverability and ROI
Roundcube - Web-based IMAP email client
ZeroBounce - Removes invalid emails from your list to prevent email bounces from ruining your deliverability.
Mailo - Mailo is an email client where you can send and receive emails to and from anyone with an email address.