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

Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.

Crisp Chat - Multi-channel customer support software

Chatrify - Chatrify provides businesses with a simple interface, user-friendly process, easy set-up options & great stuff at very competitive pricing.

Chatlio - When you have a business to run, your average instant messaging software just will not do. You need an internal presence upon which your entire team can collaborate on. Read more about Chatlio.

Olark - Real-time chat and monitoring of your website visitors through Google Talk and Jabber.