Share a single app window between two Macs

macOS can share a Mac's whole screen, but not a single window. To put just one app's window on another Mac, use an app like Waystone, which sends that window over your local network and shows it on the other Mac as a real window.

What macOS gives you

Screen Sharing shows the other Mac's entire desktop in a window. It has no option to pick one app: you get the Dock, menu bar and every open window along with it. That's what you want when you're helping someone or fixing settings, but it's a lot of screen to give up for one app.

Universal Control moves your pointer and keyboard to the other Mac instead. You can drag files and copy text across, but windows stay on the Mac whose app they belong to. You can't drag an app window from one Mac's screen onto the other.

Sidecar can move a single window, but only to an iPad being used as a second display for your Mac. It doesn't work between two Macs.

What sharing one window should mean

A shared window is only useful if it behaves like the rest of your windows. That means it sits on your desktop rather than inside another window, shows up when you press Cmd-Tab or open Mission Control, can be moved to another Space and tiled, and takes your clicks and typing directly. Anything less, and you're back to looking at a remote desktop in a box.

Share one window with Waystone

Waystone does exactly that. The app keeps running on its home Mac, and its window appears on the Mac you're using as a native window.

1. 1
   Install Waystone on both Macs. It's a menu bar app. On the Mac that shares its apps, allow Screen Recording and Accessibility when asked, so Waystone can show the window and pass your input to it.
2. 2
   Pair the Macs with a code. They find each other on your local network. Pick the other Mac and type the six-digit code it shows. You only do this once.
3. 3
   Pick the app. Waystone's menu bar list shows the apps the other Mac shares. Pick one and its window opens beside yours.

How the window behaves

• It's in Mission Control, Spaces and Cmd-Tab, and tiles like any other window.
• Mouse, keyboard and scrolling go straight to the app, and hover and tooltips work.
• If the app opens another window, such as a new email or a save dialog, it opens on the Mac you're using too.
• The clipboard is shared in both directions.
• Resizing it resizes the app on its own Mac, so content reflows. It stays sharp between displays with different scaling.
• Each app's Dock badge, like an unread count, shows in Waystone's list, so you know when to open it.

When one window is the right amount

Sharing a single window suits apps you want to glance at and reply to while you work on the other Mac: mail or chat that's signed in on the laptop, a browser with the right profile, or a heavy app that should keep running on the desktop Mac. You get that one app beside your own windows, and the rest of the other Mac stays out of the way.

When you need to change settings, find a file or use several apps at once on the other Mac, Screen Sharing is still the better tool, and it's built in.

You decide what's shared

Each Mac chooses which of its apps the other can open, in Waystone's sharing settings. Block an app and any of its windows open on the other Mac close straight away. The Macs talk directly over your local network, encrypted, with no account, servers or relay, and nothing outside your network can reach them.