For Windows, Faststone Capture 5.3 is a free (for noncommercial use) lightweight application allowing you to take screenshots (pictures) of your desktop.
It allows you to easily take a picture of the current window, the selected window/object, a rectangular region, a freehand region, full screen, and scrolling regions (like a webpage in a web browser). It’ll allow you to save or annotate the image in the same dialog, eliminating the need for pasting into Paint. Other features include a magnifier and a screen color picker.
