Snaplr is a simple way to capture and annotate your desktop's activity. Its Free to download, a great addition for your email/collaboration tool.
Snaplr, however, has a limited set of features when it comes to post-screenshot editing features but it makes taking and editing screenshots extremely easy. For example, it allows you to draw circles and rectangles of defined color over the image to point out certain area of image. The Pencil, Arrow and Text tools will help you annotate significant parts of the screenshots.
Snaplr interface is designed to be minimal. You will find the screen area capture mode along with some image editing tools. To begin, hit Take Screenshot to capture the screen area.
DownloadSnaplr: Take, Edit And Annotate Screenshots