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

Google Forms - Simple web forms from Google.

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.

Survey Monkey - Create and publish online surveys in minutes, and view results graphically and in real time. SurveyMonkey provides free online questionnaire and survey software.

Zendesk - Zendesk is a beautiful, lightweight help-desk solution.

Qualtrics - Qualtrics is the most trusted research platform, helping brands make crucial business decisions. From surveys to insights to action.