Freeware, Universal binary, only OS X.4 Tiger or higher, Leopard compatible.
If you want to change the format of the screenshots (command/Shift/3 or 4), you can do that very easily with ScreenShotFormatX.
The choices are BMP, GIF, JPEG 2000, JPG, PDF, PICT, PNG, PSD and TIFF. See here the screenshot of the app.
