According to 9to5Google, a bug report (currently inaccessible) about Chrome Incognito tabs leaked the desktop interface for the upcoming AluminiumOS, Google’s merging of ChromeOS and Android.
In their previous leaks they called it Aluminium, likely to keep consistent with Chromium. It might just be the code name though, we’ll have to wait and see what the final name is.
The OS is listed as Android, so it’s probably the case that Aluminium OS is just a renamed future version of Android that has a working desktop mode. We can’t know until it officially releases. If it is just Android, grpaheneOs is probably going to make a variant of it.