Windows has this builtin capability to make freeform screenshots via Windows-Shift-S. The image illustrates what I mean by freeform: Draw a polygon on screen and only capture that.
As far as I know, nothing on Linux provides this capability. Shutter is generally considered the most advanced screenshot app but it can only do “rectangular” areas.
Maybe I missed some app though?
Never mind freeform, I want to take a screenshot with a menu open without the menu disappearing before the screenshot is taken. I hit Print Screen and it vanishes.
Some apps provide a timer. Not as convenient though, of course.