A programming language created by Microsoft that serves a stepping stone for beginners from block-based coding languages to more complex text-based languages.
When you download the zip file for the Lit-Dev extension and it extract it you will have a folder that shows LitDev V1.2. There you will find another folder that says client-server. There you will find two .sb programs. One is for the client and the other is for the server. There are some other programs there, but I think these are the ones that you need for chat.