Following on from the “Double Line” request, I have found a couple of times that it would be really handy if the rectangle I was drawing would take the starting ‘click’ to be the mid-point of the rectangle:
Click to start, then holding [ctrl] would mirror the drag on the x axis and [shift] wold mirror it on the y axis, Holding both would mirror in both and make the starting click the centre-point of the rectangle. (Kind of like the scale tool does)
Typed in numbers to define the x and y would centre the rectangle on the relevant axis.
(Perhaps if a rectangle was created this way “Guideline points” could also be placed at the mid-points of the lines that intersect the mirror line - giving an easy “snap point” for future geometry)