The command line is a text-based interface used to manipulate and interact with a computer. The command line interface has looked roughly the same like since the days of text terminal machines, despite the vastly improved hardware available today. The Terminal emulator application on OS X looks like this:
The Terminal application on OS X

Steven Wittens has taken the Terminal application and used his considerable kung-fu to slam it face first into the WebKit rendering engine that the Safari and Chrome browsers use to display HTML. He calls it TermKit and it looks like this:
A front-end for the Terminal application built in WebKit

All I could say was “Fucking Wow”. Mighty impressive work, eh?

I can imagine command line newbies becoming very productive very quickly with a rich interface like this. But my sense is that after reaching a certain level of proficiency, you will always go back to the plain ol’ vanilla interface without all the hand holding.