Source: http://liliputing.com/2014/12/crouton-ch...

This lets you switch between Chrome OS and Ubuntu simply by changing browser tabs. you can even resize the window so you can run Ubuntu apps in one browser tab while surfing the web in another.

All you need is a Chrome OS device that’s been set to developer mode (it doesn’t matter if you’re using the stable, beta, or dev channel of Chrome itself, you just need to be in developer mode).