Neocities.org
I've added support for custom user flairs & custom commands to every chat. Currently, it's not very documented but you can play around with some of these new features at https://message.neocities.org
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Both user flairs & commands are set in JavaScript, you can use CSS to customize your created user flairs. Commands are executed in JavaScript on the PARENT site (your site) and not inside the iframe.
I can see where I'm making use of this