DrawIt 


DrawIt is an interesting Mac OS X image editing application that sports both layer support and vector tools, plus a very intuitive group drill-down feature. It has its own document format, and only exports to JPEG, GIF, PNG or TIFF (i.e., no way to get your layered document into Photoshop or any other app that supports PSD format).

Still, it is a very simple, effective and straightforward way to achieve most simple drawing and annotation tasks with a pretty good degree of control over the final result.

A freeware “lite” edition was released on Feb 2008.