GrabNDrop is a free screenshot tool with an emphasis on speed and simplicity.
The program only supports one capture type - a freehand rectangle - but this is at least well implemented. As you click and drag the mouse, GrabNDrop displays its dimensions in pixels, and when you've finished, the capture area may be freely moved and resized as necessary.
Press Enter and you're able to annotate the grab, though only with a freehand "pencil" tool.
GrabNDrop's main feature is that, when you're done, you're able to transfer the image by simply dragging and dropping it into your target application. That could be a handy time-saver in some situations, as there's no File > Save, File > Open steps, and no capture files left cluttering your drive later.
You can choose to keep your captures as files if you prefer, though, and an "Email" button allows you to send the current shot by email.
GrabNDrop is distinctly short on features, but the ability to adjust your capture area is handy, and transferring your captures by drag and drop can be convenient. It's also open source with no adware, and safe to try, if you're interested.