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
HelpScout - Help Scout is a simple, straightforward way to provide excellent support
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
Otr.to - A secure peer-to-peer chat in your web browser.
ChatWoot - Open-source omnichannel customer engagement platform
Skype - Stay in touch with your family and friends for free on Skype. Download Skype today to chat and call on desktop and mobile.