spacedesk is not available for Mac but there are some alternatives that runs on macOS with similar functionality. The best Mac alternative is Duet Display. It's not free, so if you're looking for a free alternative, you could try Deskreen or Weylus. If that doesn't suit you, our users have ranked more than 10 alternatives to spacedesk and eight of them are available for Mac so hopefully you can find a suitable replacement. Other interesting Mac alternatives to spacedesk are Air Display (Paid), iDisplay (Paid), TwomonUSB (Paid) and Splashtop Wired XDisplay (Paid).
Turn your iPad/iPhone or Android tablet or smartphone into a convenient side monitor for your Windows or Mac desktop. iDisplay is a universal app specially optimized for iPad, iPhone, iPod Touch, and Android devices screens.
Some users think iDisplay is a great alternative to spacedesk, some don't.