Any way to rotate the ruler/straight edge?
No options or configurations seem to work with my Wacom Intuos touch or wheel. Computer itself has no touch.
You can use R+Stylus to rotate the Ruler.
Is there an alternative solution for a mouse?
I just tried to hold down R and all three mouse buttons and nothing worked.
It's currently not supported but we are working on enabling it as well.
this doesn't work, at least on Windows. I found that I can move the ruler with the stylus, but I haven't found a way to rotate it.
Correction: I just had an outdated Wacom Tablet. I just purchased the newest Intuos Pro, and it does work!
For those trying to do this on a Windows desktop and having trouble, something I had to figure out was that the ruler has a pivot point. You can only rotate it at the pivot point. Hold down R and press down on the ruler with your drawing pen. You'll see a little blue box pop up with the current angle of the ruler. By letting go of R, you can can then use your pen to position the pivot point where you want it. Hold down R again, and press down on the ruler with your pen at the pivot point. This will let you rotate it. This works with a mouse as well, at least on Windows 10.
Minor correction: The box is blue on 45 degree increments (0, 45, 90, etc). From there it can only be rotated at the box. If it's on a different angle, the box is black and you can rotate it from any where on the ruler by holding down R and dragging the ruler to the desired angle. However, mine snaps to those 45 degree increments when I get within about 3 degrees of them, so fine grained control near those increments seems to be impossible for now.