CMD + N -> Open a New Window.

Shift + Click on a link -> Opens Document in a New Window.

CMD+A -> Select All. (depending on context: draft or comment or document)

CMD + , -> open settings window

CMD + {LeftArrow,RightArrow} -> navigate backwards or forward

CMD + B -> toggle left sidebar

CMD + {1,2,3,4} -> toggle accessory panels (depending on the order)

CMD + E -> Edit a document