Messenger for Mac - Facebook Messenger wrapped up as a desktop app
Freshservice - Freshservice: the one-stop cloud solution for all your IT management needs.
Chat for Mac - Facebook Messenger & Chat on your Mac
Freshdesk - Freshdesk is a cloud-based customer support software that lets you support customers through traditional channels like phone and email, social channels like Facebook and Twitter, and your own branded community
Chatty - Chat with strangers all around the world in Messenger
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.