So Yeah. It's not a kindle tool, It's a viewer for the x11vnc that I run on the kindle.
there is a build for the x11vnc on here (I just built my own) seaniko provides one...
Then I vnc into that (opening port 5900 with iptables along the way) from another machine (non kindle) and take the screenshots. (In this case with gvncviewer)
Hope that's nice and clear.