RemotePlay 7.5 for Mac could be downloaded from the developer's website when we last checked. We cannot confirm if there is a free download of this app available.
According to the results of the Google Safe Browsing check, the developer's site is safe. Despite this, we recommend checking the downloaded files with any free antivirus software. The program lies within System Tools, more precisely Remote Computing. This free Mac application was originally developed by Sony Interactive Entertainment Inc.
From the developer:
The PS4 Remote Play application allows you to control your PlayStation®4 system from your computer. With this application installed on your PC or Mac, you will enjoy immersive PlayStation® gaming while being connected remotely to your PS4™ system. The app requires a computer with either of the following operating systems: OS X Yosemite or OS X El Capitan.
You may want to check out more Mac applications, such as Splashtop Streamer, which might be related to RemotePlay.