ZenTangle: I like the whole idea behind Zentangles, from using a pen, because there are no mistakes, only opportunities to think creatively in the moment, to not using a ruler because, "If you set out with a ruler to find something that fits your expectations, what will you do if you encounter something that exceeds your expectations? Would you even notice it?" zentangle.com
"Almost anyone can use it to create beautiful images. It increases focus and creativity while providing artistic satisfaction" zentangle.com
Official website: http://www.zentangle.com/
Pattern ideas: http://tanglepatterns.com/tag/zentangle
More sources: http://www.squidoo.com/how-to-zentangle