In the crop options, there’s an option to select keeping the original ratio, “custom” which just lets you freely crop independently in each direction, or a selection of specific crop ratios.
I have a particular obsession with the Golden Ratio, and often tend to try to crop my images to fit Golden Rectangles. It would make me happy if the Golden Ration was among the built-in ratios. It can be roughly defined as 1:1.618; or more precisely calculated as 1:(0.5+√1.25).
Perhaps even better, yet, would be to allow users to edit the list of prefabbed ratios, to include those of their choice, and to remove those for which they have no use.