Usually OS X application can have multiple active windows. One can see the list of opened windows in application Window menu bar, and change the focus by selecting one of them. I was searching for some OS X keyboard shortcut to do this without mouse. There are several ways to do this (https://support.apple.com/kb/HT1343), but I find these two the most convenient:
- Control-F4 Move focus to the active (or next) window
- Shift-Control-F4 Move focus to the previously active window
The important thing is that the cycling is done through all windows of all opened applications - like a “better” alt-tab.