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
PC-Duo Remote Control - PC-Duo: fast, secure and centrally managed remote control.
ChatWoot - Open-source omnichannel customer engagement platform
ServiceWise - Web based help desk management software
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.
Salesforce Service Cloud - Service Cloud integrates customer service with social networks and provides a self-service customer portal and knowledge base system.