Open source alternative to Duet Display, Luna Display and iDisplay
Last verified
Transform your iPhone, iPad, or spare Mac into a true second monitor for your Mac over USB or WiFi. GPL-3.0 licensed, no account and no subscription required.
Any iPhone on iOS 16+ or iPad on iPadOS 16+ becomes a second extended display: landscape for a browser or editor, portrait for logs or a chat window. Works even when the device belongs to a different Apple ID, such as a partner's iPad at a shared desk.
You need audio forwarded to the secondary display, multi-touch gestures beyond two-finger scroll, hardware keyboard passthrough, or Apple Pencil pressure input. Those features are not yet available.
Portrait mode rebuilds the virtual display as a vertical rectangle at native resolution when the phone rotates. Suits log tailing, terminal output, documentation reading, and narrow vertical interfaces. Touch input lets you scroll on the device screen without leaving the keyboard.
You need frame-perfect latency for video editing, gaming, or drawing. Apple Pencil pressure and tilt support is roadmapped but not yet shipped.
Install OpenDisplay Receiver on a spare Mac running macOS 12+ and the sending Mac gains a full Retina extended display. Any Mac from around 2015 that runs macOS 12 Monterey qualifies. Thunderbolt Bridge, Ethernet, and USB-C wired connections are all supported alongside WiFi.
The spare Mac cannot run macOS 12 Monterey. The receiver requires at minimum macOS 12, which excludes Macs older than around 2015.
Corporate or family setups where the iPhone and Mac belong to different Apple IDs lock out Apple Sidecar entirely. OpenDisplay has no Apple ID requirement and pairs over a direct local connection with no account linking required.
Your organization restricts installing apps from outside the Mac App Store on managed devices. The Mac sender cannot ship through the Mac App Store because CGVirtualDisplay is a private API, so it requires a direct download from GitHub Releases.
Mac users who want a second monitor have three mainstream options, each with a meaningful restriction. Apple Sidecar is free but iPad-only, requires both devices on the same Apple ID, and only works on Apple-approved hardware pairs. Duet Display pioneered third-party tools for years but moved to a subscription. Luna Display achieves low latency through a dedicated hardware adapter, but that dongle costs extra and only works with specific Mac ports.
The result is that someone sitting next to a capable iPad or a spare iPhone has no free, open path to use it as a second screen if the devices are on different Apple IDs, if they prefer an iPhone over an iPad, or if they are unwilling to pay a recurring fee for a one-time hardware setup.
Streams over the Lightning or USB-C charging cable via macOS's built-in usbmuxd with no tunnel tools required. WiFi mode uses Bonjour for automatic device discovery; pick the device from a dropdown with no IP address entry. USB mode charges the device during use and achieves the lowest latency.
VideoToolbox encodes the display stream in real-time hardware H.264 mode with TCP_NODELAY and frame-drop backpressure. Instant keyframe recovery prevents freeze frames on packet loss. At 18 Mb/s, the stream fits within USB 2.0 bandwidth, so a standard data-capable USB 2.0 cable is sufficient.
The Mac creates a virtual display sized to match the device panel pixel-for-pixel at @2x HiDPI. Text and icons appear at the same sharpness as on the physical device. No downscaling introduced by the encoding pipeline, so a 6.1-inch iPhone screen reads as clearly as a native display.
Tap on the iPhone or iPad to click, drag to drag, and use a two-finger swipe to scroll. The Mac receives these as native mouse and scroll events via Accessibility API injection. Input works in both portrait and landscape orientation across all connected devices.
Rotate the device and the virtual display rebuilds at portrait resolution, producing a vertical monitor suited to log files, chat apps, or documentation. Up to three simultaneous devices have been tested; each appears in macOS System Settings as an independent extended display that can be freely arranged.
Install the separate OpenDisplay Receiver app (macOS 12+) on an older Mac and it becomes a second extended display for the sending Mac. Connects over WiFi, Thunderbolt Bridge, Ethernet, or USB-C data cable. The sender switches to the wired cable automatically when plugged in mid-session.
Both tools extend the Mac desktop onto an iPhone or iPad over USB or WiFi. Duet Display pioneered this approach for iOS and was the leading third-party option before moving to a subscription model. OpenDisplay provides the same core capability for free.
| Feature | OpenDisplay | Duet Display |
|---|---|---|
| Price | Free (GPL-3.0) | Subscription |
| iPhone support | Yes | Yes |
| iPad support | Yes | Yes |
| USB wired | Yes | Yes |
| WiFi | Yes | Yes |
| Open source | Yes (GPL-3.0) | No |
| No account required | Yes | No |
OpenDisplay is the better choice when cost is the deciding factor or when you want an auditable, subscription-free tool you can build from source. Duet Display remains relevant if you need a more mature tool with a longer track record across macOS major versions or enterprise support options. Duet has shipped through more macOS release cycles, which matters if stability across OS upgrades is your primary concern.
Luna Display ships a small hardware dongle that plugs into your Mac's USB-C or HDMI port. The dongle handles transport, enabling Luna Display's app to stream the Mac desktop to an iPad or another Mac at low latency. OpenDisplay matches the core use case using the charging cable you already own.
| Feature | OpenDisplay | Luna Display |
|---|---|---|
| Price | Free (GPL-3.0) | Hardware dongle + app |
| iPhone support | Yes | Yes |
| iPad support | Yes | Yes |
| Wired USB | Yes | No (dongle provides its own link) |
| Open source | Yes (GPL-3.0) | No |
| No extra hardware required | Yes | No |
OpenDisplay is the better choice for anyone who does not want to purchase hardware and is willing to use an existing USB cable. Luna Display is worth considering when you need the most consistent low-latency profile across macOS versions, because Luna's own hardware handles transport without depending on Apple's private CGVirtualDisplay API.
Building from source on macOS 14+ requires Xcode 15+, a free Apple developer account, and the xcodegen setup tool.
```bash
brew install xcodegen
git clone https://github.com/peetzweg/opendisplay.git
cd opendisplay
./generate.sh
```OpenDisplay is free to download and use with no subscription, no account, and no in-app purchase. It is funded by voluntary Ko-fi donations. The source code is published on GitHub under GPL-3.0, so you can also build it yourself for free using a free Apple developer account.
macOS shows the screen-recording privacy indicator for any app that captures the screen, including Duet Display, Luna Display, OBS, and Zoom. Apple Sidecar avoids it because it is built into the operating system rather than running as a user-space app. The indicator cannot be suppressed by a third-party app; it is a macOS privacy feature that confirms a capture session is active.
Possibly. The Mac sender uses CGVirtualDisplay, a private CoreGraphics API. Apple could change or remove it in a future macOS release without warning. The same risk applies to every virtual-display product that does not use dedicated hardware, including BetterDisplay and DeskPad. The capture and streaming pipeline uses only public macOS APIs and would be unaffected; only virtual display creation depends on the private API.
GPL-3.0. You can use, study, adapt, and distribute OpenDisplay, including for commercial purposes. If you distribute a modified version, it must remain open source under GPL-3.0 with the original attribution intact, so improvements flow back rather than into closed forks. Releases up to v0.4.x were MIT-licensed and remain available under those terms.
Yes. OpenDisplay pairs directly over USB or WiFi with no Apple account requirement on either device. This is the main practical advantage over Apple Sidecar, which requires both devices to share the same Apple ID and therefore cannot be used with a partner's iPad or a corporate-issued iPhone.
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