Draw everything with one line.
Connect all the points with only one line.
This is 'one-line-drawing' made without your hands off from the line.
There are various modes you can choose.
You can get lots of fun from 'one-line-drawing', 'double point(a point that can be used twice)', and 'jumping point(a point that can move to another point)'.
It's not quite simple. You can use line just one time in the beginning but after that you can use lines twice or threetimes and you can jump to another point!
Let's have fun!