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
Callpage - Turn website visitors into sales calls. Use CallPage and provide immediate free phone callback to your leads in 28 seconds.
ChatWoot - Open-source omnichannel customer engagement platform
Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Novocall - Novocall converts web visitors into sales calls in seconds.
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.