Only the backend?
Piece of cake, depending on what you need or have have resources for, i can make the backend based on:
Websockets
WebAPI (RESTfull)
or just normal sockets (if chrome extensions support it)
I have a lot of backend experience so far, and im most familiar with C# (.Net Core, so it can run on a linux server) ASP.Net which is great for small and large scale projects that need a backend