How can I switch among application windows using Cmd/Opt + 1/2/3... etc, like on Unity or KDE?

Why? This is especially handy if you often switch among the same few apps, e.g. a browser, a file manager and an IDE, but also have other apps open, so Alt+Tabbing to the desired window would take more time.

That keyboard shortcut saves me probably 5 seconds per minute on the average, so ~40 minutes a day, and it's supported by Windows as well.