Exceljet

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Redo last action

Windows shortcut 
CtrlY
Mac shortcut 
Y

This shortcut will allow multiple levels of redo's; each time you use it Excel will step forward one level. Also, with certain actions (e.g. deleting a row), Excel will perform that action again. So, in some cases you can use this shortcut to quickly perform the same action again multiple times.

On Windows, F4 also works.