The 6.3.1 version of AirPort Utility 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. This free software for Mac OS X is a product of Apple Inc. We recommend checking the downloaded files with any free antivirus.
From the developer:
Note: Most recent release available only within OS X 10.11 El Capitan update.
Use AirPort Utility to set up and manage your Wi-Fi network and AirPort base stations, including AirPort Express, AirPort Extreme, and Time Capsule. See a graphical overview of your Wi-Fi network and devices. Change base station and network settings, or manage advanced features such as security modes, wireless channels, and more.
You may want to check out more Mac applications, such as toggle-airport, Airport-Firefighter-Simulator or Airport Mania: First Flight, which might be similar to AirPort Utility.
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