Here is a Mac OS X port of GCNcrypt. GCNcrypt is a tool to encrypt and decrypt Gamecube Action Replay codes. The original program was written by Parasyte and the source code was released under the GPL.

Download 1.5.1 (Universal Binary 64-bit Intel + Apple Silicon)
macOS 10.9 or higher is required.

Old version:
Download 1.5 (Universal Binary PPC + 32-bit Intel)
Mac OS X 10.4 or later is required.