I created a new version: UI Sketcher (code here)

It only has two modes now: selection and drawing. Drawing horizontally created a line, anything else creates a rectangle. Later I might add text and the ability to draw in figures (e.g. to create icons) but for now I want to find out if the basic concept works.
Not working yet:
- Keyboard shortcuts
- anything not a rectangle or line
- Two bugs: Lines can’t be resized, no zoom/pan in drawing mode.
Possible feedback: I currently try to get the very basics right. What I am most interested in is: Does the tool, in its current form do something useful? How is the “feel” of “look and feel” for you? If there would be one feature to add, what would it be?