Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Aboardly - IFTTT for automated customer emailing
ChatWoot - Open-source omnichannel customer engagement platform
indemandly - Live chat 2.0: Customer messaging that converts
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
Twixor - Customer communications made interactive and dynamic!