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
tawk.to - tawk.to is a free live chat app that lets you monitor and chat with visitors on your website or from a free customizable page
Survicate - Collect feedback on your website and find out more about your visitors.
Userlike - Userlike is free live chat software for website and mobile support.
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.
Promoter.io - Promoter is designed to capture actionable and accurate customer feedback that reduces churn and drives growth