Luna Display, the solution that lets you use an iPad as a secondary display for your Mac, now works Mac to Mac. Announcing the new functionality in a blog post, Luna Display says that the feature works between any combination of iMacs, Mac minis, and MacBooks running on macOS 10.8 Mountain Lion or later.

In a tweet, Luna Display CEO Matt Ronge said that the functionality was a direct response to being “sherlocked” by Apple’s new Sidecar feature, which builds much of Luna Display’s functionality natively into macOS Catalina. Apple’s first-party solution only lets you use iPad tablets as a secondary display.

The new functionality should help you find a use for any old Mac lying around, which you might have been tempted to sell or recycle. Over on Daring Fireball John Gruber notes that the feature will be especially helpful for anyone who owns an older 5K iMac, who now has the option of pairing that computer’s excellent display with some more modern hardware.

Luna Display isn’t the only company that’s being challenged by Catalina’s Sidecar. Duet offered a similar Mac to iPad screen sharing app (without that silly dongle), and has responded by beefing up its support for non-Apple hardware. It already worked with Windows PCs, and earlier this month it added support for Android devices.

In order to use Luna Display’s new Mac-to-Mac functionality you’ll need two Macs (obviously), and one of Luna’s $69.99 USB-C or Mini DisplayPort dongles. Your host machine will need to be running macOS 10.11 or later, while the secondary Mac will need to be running macOS 10.8 or up. You can find a full list of instructions on how to get the functionality to work on Luna Display’s site.