Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
Drift - A messaging app that helps you grow your business.
Smallchat Beta - Slack integration for chatting with visitors to your website
LiveChat - LiveChat - premium live chat software. Approach customers directly on the website, make connections and drive more sales using LiveChat.
Firehose Chat - firehosechat.com
Olark - Real-time chat and monitoring of your website visitors through Google Talk and Jabber.