Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Talkus - Chat with your website users from Slack
Speaklyn - Website visitors chat with you on Facebook Messenger
Firehose Chat - firehosechat.com
Drift - A messaging app that helps you grow your business.
Chatra - Live chat software that helps to increase revenue and collect feedback providing an easy way for website owners to talk to visitors in real time.