Plugin Alliance Purple Audio MC 1.5.1 could be downloaded from the developer's website when we last checked. We cannot confirm if there is a free download of this software available. We recommend checking the downloaded files with any free antivirus. This software was originally developed by Plugin Alliance. The program is included in Multimedia Tools.
From the developer:
The MC77 employs Field Effect Transistor (FET) technology for gain reduction allowing for large amounts of limiting without introducing severe distortion. Its remarkably quick attack time, flexible release, four ratios and multi-button modes allow the MC77 to deliver everything from well mannered and transparent dynamics to full-on brick wall stopping power.
You may want to check out more software, such as Alvas.Audio for.Net Core, ImTOO DVD Audio Ripper or Audio Converter Pro, which might be related to Plugin Alliance Purple Audio MC.