The concept of a Mac doubling as a separate display isn’t new, and Luna Display has actually been offering that feature for a while now. It might seem like the company’s software could be rendered obsolete with Sidecar, but they are actually stepping up their game with the introduction of a new Mac-to-Mac mode.
Basically, what this new feature does is that it allows users to turn an existing Mac computer into a secondary display. According to Luna Display, “Our all-new Mac-to-Mac Mode allows you to use any Mac as a second display. Finally, you can give purpose to your old Macs lying around! No need to have any idle devices. The combinations are nearly endless.”
However, to take advantage of the feature, you will need to buy the dongle that will allow the feature to work. The dongle will be available for USB-C or Mini DisplayPort and will be priced at $70. It should also be noted that not all Macs are compatible, and that the secondary Mac computer that will be used as the display will need to run macOS 10.8 Mountain Lion or later.