OpenDisplay is an open-source macOS app that turns an iPhone, iPad or spare Mac into a true second monitor for your main Mac, connected either over the USB cable or over WiFi. It is written for people who already own an idle Apple device and do not want to pay a monthly fee, buy a hardware dongle, or accept the pairing rules that come with Apple's own Sidecar. Developers who work on macOS screen capture, video encoding or device transport will also find it worth opening, because the Swift source for all of those pieces is public under GPL-3.0.
What it does
The core promise is display extension rather than mirroring. macOS treats the connected device as a real external monitor: you can drag windows onto it and arrange its position in System Settings alongside your other screens. Mirroring is available too, as a mode you choose rather than the only thing on offer.
Around that, the project lists:
- Retina-sharp HiDPI output, so text on the phone or tablet is not a scaled-up blur.
- Touch and scroll input, so tapping the device screen clicks, drags and scrolls on the Mac.
- A wired USB path over the Lightning or USB-C cable for the lowest latency, with no network involved.
- A WiFi path for when you would rather not run a cable.
- No account, no Apple ID matching between the two devices, and no subscription.
The last point is the practical reason the project exists. Sidecar is free but needs both devices signed into the same Apple ID, does not support iPhones at all, and only works on supported hardware pairs. OpenDisplay drops all three of those conditions.
How it works
On the Mac side, the app creates a virtual display — that is what makes macOS believe a second monitor is attached — captures its contents, and encodes the frames as H.264. The GitHub topics name the Apple frameworks behind that: ScreenCaptureKit for capture and VideoToolbox for hardware encoding and decoding. The client app on the iPhone or iPad decodes the stream and paints it, and touch events travel back the other way to be injected as mouse input on the Mac.
The wired transport is the interesting part. Instead of shipping a helper daemon or asking you to configure a network, the USB mode rides on usbmuxd, the multiplexing service already built into macOS for talking to iOS devices over the cable. You plug the device in and the stream has somewhere to go — no WiFi jitter, no IP addresses, no pairing dance.
Getting started
The repository is a normal public Swift project on GitHub, with a project website and a quick-start section in its README as the entry points. The license is GPL-3.0, which matters if you plan to build on it: derivative work has to stay open as well.
The README is also explicit about wanting contributors, with the argument that the genuinely hard parts — virtual display creation, the low-latency H.264 pipeline, USB transport and input injection — already work, so anyone who was about to start their own version should add to this one instead. The repository was created in June 2026 and was still being pushed to in September 2026, and it has drawn roughly 3,500 stars and 247 forks in that time, so activity and attention are both there.
When to use it / when not
It fits when you have a spare Apple device and Sidecar will not cover you: an iPhone rather than an iPad, two devices on different Apple IDs, a hardware pair Apple does not bless, or simply a reluctance to keep paying Duet Display every month. It also fits if you want to read, and possibly change, the code that is streaming your screen.
It does not fit if your host machine is not a Mac — everything here is built on macOS frameworks and Apple's USB stack. If Sidecar already works for your particular Mac and iPad pair, the gain is mostly philosophical. And a project this young, on a GPL-3.0 license, is a different proposition from a commercial app with a support desk: treat rough edges as part of the deal.
Alternatives
The three products OpenDisplay measures itself against are named in its own README. Apple Sidecar is free and deeply integrated but restricted by Apple ID, device support and the absence of iPhone support. Duet Display is broad and mature but has moved to a subscription. Luna Display gives excellent results but requires you to buy and carry a hardware dongle. OpenDisplay's pitch is the fourth corner none of them occupy: free, open, no account, no dongle.
Anyone with a drawer full of retired iPhones and iPads should take this seriously, because it converts dead hardware into working desk space for nothing. Developers curious about how a second monitor is faked on macOS get an unusually complete reference implementation in the same download: virtual display, capture, encode, transport and input injection, all in readable Swift and all currently maintained.