Sequator

Sequator is a free software which can track stars on multiple pictures, align them, and stack the pictures.

By stacking non-blur star images in short-time exposures, you can obtain a result almost the same as a long-time exposure, like on an equatorial mount. However, Sequator can control the exposure properly by automatic brightness or HDR-mode output, in 16-bit TIFF for further post processing. Additionally average random noises, rather than over-exposed on a physical equatorial mount.