This wonderful extension is almost a replacement for Chrome's app windows: you can run webapps in their own window, as if they were a native app and not a browser tab. The pop-out window has none of the browser GUI (address bar, tab bar, bookmarks), just the plain content. I was searching for something like this for so long!

Remember to enable the "Tab menu item" so that you can move a tab directly to a popup window :)

While the extension is quite young, it already works very well. I've looked at the source code and it's all very reasonable. The only thing that could be improved is more locales (as of v0.0.4, only en and zh_TW are supported).