UseResponse - Open-source, self-hosted customer feedback software, live chat and helpdesk system that you can install on your server. Organize documentation using knowledge base and get feedback from social networks with centralized system
MailChimp - MailChimp is the best way to design, send, and share email newsletters.
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.
Elastic Email - Elastic Email is an all-in-one email delivery platform for both marketing and transactional email.
Olark - Real-time chat and monitoring of your website visitors through Google Talk and Jabber.
Zoho Campaigns - Smart email marketing software that helps you reach your target audiences, engage in a personalized way, and grow your brand presence.