Image Stacker 2.1

Image Stacker is a windows program, but can also be run from the command-line and easily incorporated into scripts and batch files.
Image Stacker combines or "stacks" multiple images into a single image, using one of several different blending methods. Image Stacker can be used for a variety of purposes, but its primary purposes are (1) to create very long exposures (longer than would be possible using any single exposure) (2) to create star-trail images and (3) to reduce the appearance of "digital noise".