GCMTools 0.3 for Mac was available to download from the developer's website when we last checked. We cannot confirm if there is a free download of this app available. The program is included in Games. We recommend checking the downloaded files with any free antivirus.
From the developer:
GCMTools are a suite of tools to basically rip apart your gamecube games and put them back together however you wish. Its aim is to give you access to everything so you can modify and hack your games to your wildest dreams. Currently, there are 5 executables that are part of this package: gcmtool- for auditing, extracting and editing Nintendo GameCube DVD images (.iso or .gcm).
You may want to check out more software for Mac, such as World of Warcraft Interface AddOn Kit, Virtual Combat Cards or Endarchy, which might be similar to GCMTools.