Some applications that implement MDI provide Ctrl+Tab to switch between "Documents" under the same application instance. e.g. MS Office. But this is not a windows feature and is application dependent. For other software there are different short-cuts. e.g. Firefox does not provide this feature but there is an add-on that adds the functionality.
Additionally, here's a list of keyboard shortcuts provided in windows.
Also, there are existing discussions about Keyboard short-cuts in Windows.
Hope that helps.