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
Smooch.io for Facebook Messenger - Message your customers from Slack, Front, a bot or anywhere!
ChatWoot - Open-source omnichannel customer engagement platform
GetChat.App - Add WhatsApp chat to your website for free
Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Avochato - Text messaging for your business.