Nordvind

Puts a “wall” into a blog, where blog authors can chat. Wall can be hidden from unregistered users. 
Intended to use in community/corporate blogs, for coordination between authors.

MBlog

minnitchat

Minnit Chat is an easy-to-use group chat service. You can appoint moderators to watch over your chat, customize the look and feel of your chat, and increase engagement by having your users be able to talk to one another in real time!
Configure the chatroom to use Single Sign-On, and users who load the chat will automatically be logged in using their WordPress accounts. No need for additional sign-ups, onboarding, or any other steps — your users can get chatting right away!
Many other features can be enabled or disabled, including support for sending GIFs, uploading files, direct messaging between users, and more.
Get started in minutes and get chatting with Minnit!

Group chat for WordPress – Minnit Chat

Cloud-based chat using your WordPress accounts. Minnit uses SSO to allow you and your WordPress users to communicate with one another.

MBlog vs Group chat for WordPress – Minnit Chat