Postfix - Postfix is a mail transfer agent (MTA) that routes and delivers electronic mail.
Eventbrite - Discover Great Events or Create Your Own & Sell Tickets
iRedMail - A fully fledged, free email server solution, an open source project (GPL v2).
Splash - Anyone can create a Splash event, whether you're a company hosting a single event or an individual hosting a personal event like a birthday or wedding. Get Started for Free. Text goes here. X. Full Event Program.
Zimbra - Zimbra is trusted by over 500 million users to increase productivity with a complete set of collaboration tools while maintaining total control over security and privacy.
Eventzilla - Eventzilla lets you sell tickets online and manage attendees from one integrated application.