Hey, I'm the developer behind Grapevine, thanks for the mention! If anyone is interested in how the Grapevine web client works, it's all open source and written in Elixir with the front end being React/Redux.

The main application: https://github.com/oestrich/grapevine

And the telnet connection pool node: https://github.com/oestrich/grapevine-telnet