Xournal is also using CTRL-Y for Redo and CTRL-Z for Undo (coupled with U and R)

Package 13 is also using "I" for Zoom-IN and "O" for Zoom-OUT (I didn't think about a "Reset zoom" key.. mmm).

For Quit I'm using CTRL-Q (CTRL-W is usually to close the current window or the whole program is this is the last window open).

Aniello