The 3.61 version of RatHole for Mac was available to download on the developer's website when we last checked. We cannot confirm if there is a free download of this app available.
Please check the Mac app with an antivirus before launch as it is downloaded from the developer's website, and we cannot ensure that it is safe. The most popular version of the application is 3.6. The program relates to System Tools. This app's bundle is identified as com.edgesounds.RatHole. This free software for Mac OS X was originally created by Edgesounds.
From the developer:
EdgeSounds' RatHole (former GenieSys RatHole) is a free unique nondestructive universal compression utility. Its function is based on a principle of self-training neural networks.
EdgeSounds RatHole was especially designed for nondestructive compression of any files containing audio data in PCM 8/16/24 bit or IEEE_FLOAT 32 bit format.
You may want to check out more Mac applications, such as CreaDMG or GeeUnRAR, which might be similar to RatHole.