You can spend hours and hours with demoish tool. It draws all kinds of knots in many ways (start the program and go to demoA or demoB tab in top right). I guarantee you cannot be disapppointed at taking the time to download this. Quite fascinating.
http://knotplot.com/download/
Hmmm how useful it is, I'm unsure. But fun, oh yeah. Or, well I could just be weird.
Chris
reminds me a little of etch a scetch but with knots