iChat is a customizable chatting service based off of Google Firebase. All you have to do is embed the line of HTML (found in embed.html) into your HTML file, add the Firebase rules snippet (database-rules.json), and (optionally) provide some styling.
You need to have authentication set up with Firebase in order for this to work. The username displayed by iChat is the user's displayName.
More information on setting iChat up can be found here.