Scribbler Too is quite an addictive online drawing tool. It does not draw straight lines; instead strokes connect to existing lines if they are in their influence area. Try it and you will see what I mean.
Interestingly this tool creates a new drawing experience. Instead of focusing on individual lines I drew my attention to the entire image and the relation of the lines. I was amazed at the results considering that I only used a mouse to draw (which with other drawing programs creates pretty bad scrawly images).
The influence of the lines on the brush behaviour is an interesting effect that really only works in a digital environment. Below are some more drawings that I made today.