Alfred extension or equivalent that brings a single window to the forefront
If you have the full Alfred version, then you can map hotkeys to application launching and switching.



For example, as you see on the screen I've mapped option-1 for MacVim, option-2 for Chrome, etc.

If the app is not running it will launch it but more importantly if the app is running but not focused, then it will simply switch to that app.

I hope that helps!