IRC, XMPP, WebRTC, WebSocket and AJAX. Almost all common chat clients are based on one of these technologies. The most straight forward protocol to implement

IRC, XMPP, WebRTC, WebSocket and AJAX. Almost all common chat clients are based on one of these technologies. The most straight forward protocol to implement is certainly IRC. It works very well for group chats and is used by many open source projects and in house usage. FBchat and Gchat are based on a slightly non-standard XMPP, at least started from that point and turned less and less open. Maybe I am a forerunner, I used chat a lot more several years ago, and nowadays write a lot more (short) emails or just talk in person (or over VoIP with video). On the other side, we will chat/talk a lot with our personal software assistent in future.