What software do I need to view a .arf? I have a macbook pro with OS 10.

You can not directly watch ARF file on your Macbook or any other third-party platform like Windows Media Player and VLC because ARF is the proprietary format of Cisco WebEx. You should first convert it to WMV, with WebEx Network Editor, here is its offical link: https://www.webex.com/play-webex-recording.html

And then follow it

Step 1: Click on "File" and then open the ARF file you want to play on your device.

Step 2: Hit "Convert Format" and choose "WMV"

Step 3: Start conversion.

Step 4: Find the output WMV file and then use some other video converter to convert WMV to more common formats like AVI and MP4, you can make use of this article which give am exhaustive description: http://www.videoconverterfactory.com/tips/arf-converter.html

http://www.file-extensions.org/arf-file-extension

Convert webex advanced recording file to mpeg-4 video file format.

WebEx has the option to convert its ARF files to Windows Media Video format. This can be then easily converted to *.mp4 files using one of the WMV to MP4 converters.

Latest versions of Cisco WebEX also support MPEG-4 format directly, so it should be able to convert ARF to MP4 without trouble.

I don't know how trustworthy any of these links are, and the site is very cluttered. It looks designed to trick people into clicking on unrelated download links by accident. If you want to try to get the WebEx player for Mac, I'd suggest that you go directly to the Cisco site.