Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Firehose Chat - firehosechat.com
Talkus - Chat with your website users from Slack
Speaklyn - Website visitors chat with you on Facebook Messenger
Drift - A messaging app that helps you grow your business.
Callingly - Turn your website visitors into callers with a click