To use Mac-to-Mac mode, users must purchase a Luna Display dongle that plugs in to the second Mac. USB-C and DisplayPort options are available for $69.99 each, and Luna is offering 25 percent off through Friday.
The primary Mac must be running OS X El Capitan or later, while the secondary Mac requires OS X Mountain Lion or later. In addition, both Macs must be connected to the same network via Wi-Fi or Ethernet, and each require the free Luna Display app available to download on the Luna Display website.
Luna Display is pushing forward despite Apple adding Sidecar in macOS Catalina, a native solution for using an iPad as a second display for a Mac.
"With all of the hype around Sidecar, one of the biggest gripes we've heard is that it only works with a limited range of Mac models," wrote Luna Display co-founder Giovanni Donelli in an email. "That got us thinking about how we can push Luna Display to bring even more value to our Mac devices."
Apple also has a feature called Target Display Mode that allows late 2009 to mid 2014 iMacs to be used as as external display for another Mac.
Luna Display's solution includes full keyboard, trackpad, and mouse support on both Macs. The company has shared complete step-by-step instructions on how to set up Mac-to-Mac mode on its website.