Downloading PixInsight64 1.7 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 belongs to Design & Photo Tools. This Mac app is an intellectual property of Pleiades Astrophoto S.L. The following version: 1.7 is the most frequently downloaded one by the program users. We recommend checking the downloaded files with any free antivirus.
From the developer:
PixInsight is an advanced image processing software platform designed specifically for astrophotography and other technical imaging fields. PixInsight is a modular, open-architecture system where the entire processing and file handling capabilities are implemented as external, installable modules.
You may want to check out more Mac applications, such as QuickShow OSX, Stone Studio or PhotoDesireeExpress, which might be related to PixInsight64.