Downloading SAOImageDS9 8.4.1 for Mac from the developer's website was possible when we last checked. We cannot confirm if there is a free download of this app available. The program lies within Education Tools, more precisely Science. This free Mac app is a product of ds9.si. We recommend checking the downloaded files with any free antivirus.
From the developer:
SAOImageDS9 is an image display and visualization tool for astronomical data. With the Advanced View, DS9 has implemented icons that provide one-click access to many of the most common tasks: file open, region shape, bin/block/zoom, frame controls, and so much more.
In illustration mode, you can create graphics to be overlaid independent of underlying frames and color bars. You can export as PNG image or print as postscript.
You may want to check out more software for Mac, such as Gee, Arcade Math Blocks or NLVM, which might be related to SAOImageDS9.