As it's REST API powered, it doesn't. It could have been anything we wanted it to be. We just went with React & co. because we determined it'd be the best solution.
> So what does the Node powered REST API provide that PHP powered traditional Wordpress API does not?
Our REST API is PHP-powered and built on top of WordPress: https://developer.wordpress.com/docs/api/
Calypso is a React-based administration client for that API.
As far as I can tell, the node.js portion is just returning an empty admin.html, and that's where client-side React.js kicks in? It seems PHP would be able to do that pretty well, with the advantage of single technology and a more obvious approach for the self-hosted wp.org sites.
https://github.com/Automattic/wp-calypso/blob/master/docs/gu...