Speccy is not available for Mac but there are a few alternatives that runs on macOS with similar functionality. The best Mac alternative is Neofetch, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 50 alternatives to Speccy and four of them are available for Mac so hopefully you can find a suitable replacement. Other interesting Mac alternatives to Speccy are Screenfetch (Free, Open Source), Systempal (Paid) and MacCPUID (Free).
SystemPal is becoming an ALL-IN-ONE app. It is the best tool to monitor your memory/CPU usage status, CPU temperature and fan speed, network speed. It also provides a tool kit including mini music player, screen shot utility, memory cleaner.