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
Crisp Chat - Multi-channel customer support software
Survicate - Collect feedback on your website and find out more about your visitors.
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
Heeduser - Heeduser is the customer engagement platform that helps companies build better relationships with their customers and prospects, through the better online customer community
csupport - cSupport offers Live Chat support. Ideal for small businesses and Entrepreneurs Worldwide.