Last month I'm working on my own extension for Chrome. It adds two things - a much simpler new tab page and fully working interactive console. The command prompt is actually added in the DevTools panel.
I'll be honest and I'll say that I'm a bit lazy sometimes. I'm one of those developers which don't like to repeat same actions again and again. There are dozen of things which I have to do while working on a project. Very often I'm covering the development of several applications and have to switch between them. It's really annoying process. I hate to have many opened tabs in my browser, many consoles or several code editors. I always try to improve my productivity by automating tasks. I think that even switching between opened applications takes too much time.
That's right. I'm not using the terminal anymore. Instead of that I'm using Chrome. Yes, the Google's browser. There is an extension called Yez! that connects to a Node.js module via web socket. It executes the shell commands and returns the result. And even works under Windows.