Downloading MCG 3.6 for Mac from the developer's website was possible when we last checked. We cannot confirm if there is a free download of this app available. The application lies within Developer Tools, more precisely IDE. The actual developer of this software for Mac is Aggmedia Pty Ltd. We recommend checking the downloaded files with any free antivirus.
From the developer:
MCG lets you analyze your application profile data on your Mac. With its call tracing and function summaries, you will be able to detect and correct any parts of your application that are taking longer than they should. MCG requires callgrind data for your application, which can be generated in many languages, such as PHP, Ruby, and Python, or can be baked in for compiled languages.
You may want to check out more software for Mac, such as JBuddy Bot Builder, HexDecBin or Pleinpot, which might be related to MCG.