The 4.2 version of JMRI: DecoderPro 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 software lies within Games, more precisely Tools.
From the developer:
JMRI: DecoderPro is an essential utility for model railroad enthusiasts.
Modern DCC decoders are complicated beasts to program. The simple idea of "put the address in CV01" doesn't cope well when you program complicated functions using combinations of bit patterns. A friendlier interface is needed. There are programs that provide better ways of programming specific decoders.
You may want to check out more software for Mac, such as JMRI, which might be related to JMRI: DecoderPro.