I just tried the current Windows snipping tool.
Greenshot is superior in almost any way, except for two things.
One is the zoom which will come in 1.3.
But they have a nice ruler tool.
You can rotate the ruler (though it is unhandy that it only works degree by degree)
and then you can draw a line alongside the ruler.
Such a ruler would be nice in Greenshot too, that snaps drawing tools, like drawing a rectangle where one side is on the ruler, drawing an ellipsis that touches in one point on the ruler, drawing a straigth line alongside the ruler, ....