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
Chatlio - When you have a business to run, your average instant messaging software just will not do. You need an internal presence upon which your entire team can collaborate on. Read more about Chatlio.
Aircall's Zendesk App - The best phone companion for Zendesk
Crisp Chat - Multi-channel customer support software
HelpScout - Help Scout is a simple, straightforward way to provide excellent support