To close all windows of the app, press Option-Command-W. To minimise all windows of the front app, press Option-Command-M.
To view the front app but hide all other apps, press Option-Command-H. To find the previous occurrence, press Shift-Command-G.
In some apps, you can undo and redo multiple commands. You can then press Shift-Command-Z to Redo, reversing the undo command.
Command-C: Copy the selected item to the Clipboard.Command-X: Cut the selected item and copy it to the Clipboard.
