DarwinPsk 0.8 for Mac could be downloaded from the developer's website when we last checked. We cannot confirm if there is a free download of this app available. This free software for Mac OS X was originally developed by Volker Schroer. 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 software lies within Audio & Video Tools, more precisely General.
From the developer:
DarwinPsk is free to licensed ham radio operators and is a great application for PSK and RTTY communications under OSX