From the site:
What is Scapple? An easy-to-use tool for getting ideas down as quickly as possible and making connections between them. It isn’t exactly mind-mapping software — it’s more like a free-form text editor that allows you to make notes anywhere on the page and to connect them using straight dotted lines or arrows.
If you’ve ever scribbled down ideas all over a piece of paper and drawn lines between related thoughts, then you already know what Scapple does.
For MacOS X only / From the company behind Scrivener