Edit
Ctrl+ZUndo
Ctrl+Shift+Z / Ctrl+YRedo
Ctrl+ASelect all
Ctrl+DDeselect
DelClear selection · otherwise: delete layer
Ctrl+C / X / VCopy / cut / paste
XSwap foreground/background colour
DReset colours to black/white
Ctrl+Shift+IInvert selection
Shift / CtrlAdd to selection
AltSubtract from selection
Shift+AltIntersect with selection
Alt+BackspaceFill with foreground colour
Ctrl+BackspaceFill with background colour
Ctrl+IInvert
Ctrl+Shift+UDesaturate
Ctrl+Shift+LLevels
Right mouse buttonMenu on the canvas or on a layer
Layers
Ctrl+JDuplicate layer
Ctrl+Shift+NNew layer
Ctrl+EMerge down
Ctrl+Shift+EMerge visible layers
Ctrl+[ / ]Layer down / up
Ctrl+SExport
View & transform
Ctrl+0Fit
Ctrl++ / −Zoom in / out
Ctrl+scroll Zoom
Ctrl+TFree transform
Enter / EscApply / cancel
TabHide / show panels