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
Survicate - Collect feedback on your website and find out more about your visitors.
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.
Heeduser - Heeduser is the customer engagement platform that helps companies build better relationships with their customers and prospects, through the better online customer community
idea.informer - Idea Informer is a idea forum similar to uservoice or getsatisfaction.
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.