The 5.3.5 version of FlightAware 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. The application lies within Lifestyle Tools, more precisely Travel. We recommend checking the downloaded files with any free antivirus. The actual developer of this free Mac application is FlightAware.
From the developer:
FlightAware allows you to track the real-time flight status and tracking map of any commercial flight worldwide. It can also track general aviation (private, charter, etc.) in the United States and Canada. You can search by aircraft registration, route, airline, flight number, city pair, or airport code. Tracking data includes complete flight details and full-screen maps with NEXRAD radar overlay.
You may want to check out more Mac applications, such as Build-a-lot 3, XPlaneCentre or TravelRecorder, which might be related to FlightAware.