Tandem Download
  1. That old 5K iMac? One Thunderbolt cable, and it's connected.
  2. Tandem: two Macs, one desk. One picture spans both screens.
  3. 5120 × 2880: pixel for pixel, lossless when still.
  4. Only what changes is sent, compared on the GPU.
  5. The iMac's keyboard and mouse work too.
  6. A camera that follows your gaze, for FaceTime, Zoom and Teams.
  7. Brightness keys, True Tone, sleeps together, lid-closed mode, and any 5K iMac since 2014.

Download Tandem

Turn a spare Mac into a sharp, native-feeling second display for your main Mac, over one Thunderbolt cable.

Download for Mac, free

Version 1.02.2 MB DMGApple silicon and Intel

Signed and notarised by Apple, so it opens without warnings.

Set up in a minute

Install it on both Macs

It's the same app on each. Drag it to Applications and open it.

Connect a Thunderbolt cable

Tandem finds the other Mac over the link by itself, and reconnects if the cable is pulled.

Pick a role

Tandem suggests one: Extend This Mac on your laptop, Be a Display on the iMac.

Everything it does

True Retina display

Native 5K, pixel for pixel, with the usual “looks like” resolutions in System Settings. Arrangement and window positions are remembered.

Lossless picture

Anything still is sent losslessly. Moving content is compressed on the GPU while it moves, then made pixel-perfect again about 0.2 s after it stops.

Plug and play

Connect the cable and it appears. It notices a pulled cable and reconnects by itself.

Keyboard and mouse

Click on the iMac to drive both screens with its keyboard and mouse. Press and release ⌃⌥ to give control back.

Brightness follows

The iMac follows the MacBook's brightness, including auto-brightness. Brightness keys change whichever screen the pointer is on.

True Tone and Night Shift

The MacBook's colour adaptation is applied to the iMac, so the two screens match.

Tandem Camera

One virtual camera for FaceTime, Zoom and Teams that shows whichever camera you're facing, with a soft crossfade.

Sleeps and wakes together

Put the MacBook to sleep and the iMac's screen goes dark too, then wakes when the MacBook does.

Lid-closed mode

With the MacBook on power, close the lid and keep working on the big screen with the iMac's keyboard and mouse.

Behaves like a monitor

Opens at login on both Macs. The iMac can start up after a power cut and use automatic login.

Old iMacs welcome

Any 5K iMac back to 2014 can be the display, on macOS 11 Big Sur or later.

Light on resources

You won't notice it running: it uses next to no CPU on either Mac when the desktop is idle.

What you need

  • Two Macs and a Thunderbolt cable. For the full link it must be a Thunderbolt cable, not a USB-C charge cable. 2014–2015 5K iMacs have Thunderbolt 2 ports and need Apple's Thunderbolt 3 (USB-C) to Thunderbolt 2 adapter.
  • The Mac you extend: macOS 14 Sonoma or later.
  • The display Mac: macOS 11 Big Sur or later.
  • Permissions: Screen Recording, plus Accessibility for the keyboard, mouse and brightness keys. Tandem asks the first time each is needed.
  • Why not the App Store? Tandem uses system features the Mac App Store doesn't allow, so it's offered here as a download instead.
Download Tandem