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.
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
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.
Canny - Canny helps you collect and organize feature requests to better understand customer needs and prioritize your roadmap.
HelpScout - Help Scout is a simple, straightforward way to provide excellent support
GetSatisfaction - Get Satisfaction is the leading customer engagement platform that helps companies build better relationships with their customers and prospects, through the best online customer community.