Download of Starry Sky Stacker 1.5 for Mac was on the developer's website when we last checked. We cannot confirm if there is a free download of this app available. We recommend checking the downloaded files with any free antivirus. The program is categorized as Design & Photo Tools. This software for Mac OS X is a product of Ralph D. Hill LLC.
From the developer:
Starry Sky Stacker reduces noise in pictures of the night sky that are captured as a sequence of exposures taken with a modern dSLR or mirrorless camera using an equatorial mount. Starry Sky Stacker aligns the images to compensate for errors in tracking, assigns a quality estimate to each image, allows the user to select images based on the quality estimate, and composites the remaining images.
You may want to check out more Mac applications, such as Starry Landscape Stacker, Sky Sports or Sky Cinema, which might be similar to Starry Sky Stacker.