That's Death Valley Dinesh!! I just re-heard that episode on "Best of Car Talk"
Then, I discovered excalidraw[1]: it lets me sketch like lucid, but isn't nearly as polished or robust: you can throw together simple shapes, draw lines between them, and the lines stick to the shapes, so you can move them around and the lines move too. You can also group things together, and draw freehand, and also include text -- what more do you need?
The cool thing about excalidraw is that you can share your drawings, and export them as SVG files -- yay! I can version them again. You can also self-host it, which is a massive plus in my book.
/rant