Zentangles or google 'zentangle', Amazon have several books on the subject by Suzanne McNeill which are relatively cheap.
I've been practising turning my tangles into quilt tiles the one above is a 5"tile which I tried putting a bit of colour onto. The one below will is the prototype for February's Journal Page and so is 10". I wanted to see just how much a challenge I had taken on. I've started with some of the easier tangles to interpret but there are several that will be either impossible, at least for me, or difficult to quilt. This one is a quarter of a flower each month the petal and corners will be different and I hope when hung together will harmonise into a whole.
I ended up sewing the outlines and colouring some of the patterns using a black Sharpie. As you can see the quilting leaves a lot to desire but I need a lot more practise. This is going to be a real challenge but enjoyable I think.
The Sketchbook Challenge this month is 'Opposites' I did think of saying my tangles were opposite because they were done in black and white. I am going to do one on black paper with a white pen and then I might just change my mind and sketch something completely different.