It is very simple: When you run it it will create a web server (listening on port 5000) by default; when you visit that server with your browser you'll get a terminal to your system (the same terminal / user that was used to originally run the server).
Come up with an interesting idea, spend n number of days working on idea, get to the front page of hackernews, have thousands of eyeballs on your thing...Spend 0 time on the readme and have everyone take a half second glance, not know what the thing is or does and move their attention else where. Let this be a lesson to everyone to spend some time on your readme's...https://github.com/matiassingers/awesome-readme
I visited the README solely because “adorable” was a provocative word and I wanted to see a screenshot of said adorableness. Give the people what they want!
My interpretation was that it was simple, code is easy to read and it does one simple thing.
This launches a new instance of a command of your choosing for every new connection. That does not really seem like casting to me more like a remote shell, but it is adorable in some ways.
I'm sure it is an interesting engineering exercise, but I struggle to think of a situation where I would fire a browser to use the terminal instead of just opening a terminal.
The name might be a hint as to the utility. If you wanted to display your terminal on your massive television using, say, Chromecast, you wouldn't have the option, but you can "cast" a browser window.
I guess you could run the program in one of your private servers then do a reverse proxy to that from a public server. Voila: Easy terminal access to your private servers from everywhere!
Not a good idea from a security standpoint though...