Chatterino - Chatterino is a chat client for twitch chat.
Messenger for Mac - Facebook Messenger wrapped up as a desktop app
Chatty - Chat with strangers all around the world in Messenger
Goofy - A Mac app for Facebook Messenger
Restream Chat - Restream Chat is a versatile software that permits you to streamline multiple chats in one place.
Caprine - Elegant Facebook Messenger desktop app