Running Microsoft Remote Desktop on MacOS 10.8.5
Connect to Windows PC from mac OS
Mac OS X Mountain Lion 10.8.5 – Microsoft Remote Desktop Client download below
***As you know, you can no longer download Microsoft Remote Desktop from the Apple Store for your older MacOS 10.8.5, since only 10.9 is supported.
However, here is a link for a previous installer of Remote Desktop 8.0.12, which is supported by MacOS 10.8.5.