UserVoice - UserVoice integrates easy-to-use feedback, helpdesk, and knowledge base management tools in one platform that empowers users to speak and companies to understand.
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.
Freshdesk - Freshdesk is a cloud-based customer support software that lets you support customers through traditional channels like phone and email, social channels like Facebook and Twitter, and your own branded community
Olark - Real-time chat and monitoring of your website visitors through Google Talk and Jabber.
Woopra - Track your customers' web and mobile activity, forms, emails, support tickets and more, all in one place with customer analytics. Analyze and take action.
Canny - Canny helps you collect and organize feature requests to better understand customer needs and prioritize your roadmap.