THis app doesn't have any features" is selling it short!
ShiftN is by far the best tool I've found for correcting pictures which are out of plumb / true, as well as for the intended purpose of correcting distortions caused by camera angle. It is particularly good for photos of building where it has no trouble finding reference lines which should be vertical.
The automatically determined correction factors are usually quite accurate if one wants a trued-up plane projection view. However, the results sometimes look a bit unrealistic. Thanks to the offered adjustments, one can reach a good compromise between the distorted original and a pure planar projection which is pleasing to the eye.
The corrections will naturally change the borders, usually from a rectangle to a trapezoid. However, the default "save and exit" does a good job of cropping the result to a new rectangular format.