DISQUS - Disqus is a global comment system that improves discussion on websites and connects conversations across the web.
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.
Answerbase - Add a Q&A system to your website in just minutes, with Answerbase's powerful question and answer software for online communities and customer support.
Typeform - Create beautiful, next-generation online forms with Typeform, the form & survey builder that makes asking questions easy & human on any device. Try it FREE!
utterances - A lightweight comments widget built on GitHub issues.
LimeSurvey - LimeSurvey: the Online-Umfrage Tool - Open-Source Suryeys