Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates
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
MessageBird - Reach 7 billion phones in seconds via SMS, Chat & Voice. Try it for free and improve your communication.
JivoChat - JivoChat is a live chat that enables you to talk to visitors on your website
Plivo - Plivo simplifies your customer engagement.