OpenDisplay: Use Your iPad as a Real Second Monitor for Mac

TL;DR: OpenDisplay is an open-source, GPL-3.0 alternative to Apple’s Sidecar and the commercial Duet Display. It turns an iPhone or iPad into a functional second display for macOS over USB or WiFi, with low-latency H.264 streaming, Retina HiDPI support, and touch input passthrough.

Source and Accuracy Notes

• Repository: peetzweg/opendisplay
• License: GPL-3.0
• Stars: 3,607 (as of September 2026)
• Language: Swift
• Topics: duet-display, external-display, ipad, iphone, macos
• Homepage: opendisplay.app

What It Is

OpenDisplay is a native macOS and iOS application pair that streams the contents of a virtual display from your Mac to your iPhone or iPad. Once paired, the iOS device shows up in macOS as an additional display, exactly like a physical external monitor.

The features that matter for daily use:

• USB and WiFi transport. Either cable or wireless, your choice. USB is faster and more reliable; WiFi is more convenient.
• H.264 hardware encoding. Video is encoded with the Mac’s hardware H.264 encoder, which keeps latency low and CPU usage modest.
• Retina HiDPI. The iPad’s high-DPI display is treated as a proper Retina monitor, so text and UI look crisp rather than upscaled.
• Touch input passthrough. Touches on the iPad are translated into macOS pointer events, so you can drive the secondary display from the tablet itself.

The codebase is Swift end-to-end. The macOS side handles display virtualisation and encoding; the iOS side handles decoding and touch forwarding.

Why It Matters

A second display is one of the highest-impact productivity upgrades for any developer, writer, or designer. Apple’s own Sidecar is the obvious answer for Mac+iPad users, but it has real limitations: it only works on supported hardware, it ties up your iPad for the duration of the session, and it’s gone on newer macOS releases when Apple decides a device isn’t supported.

OpenDisplay is the open-source answer to that frustration:

• GPL-3.0. The code is genuinely open. You can read the implementation, fork it, and adapt it.
• Hardware-friendly. Runs on Macs and iPads that Apple’s official tools no longer support, because the implementation is independent of Apple’s first-party framework.
• No subscription. Sidecar is free but limited; Duet Display charges a subscription. OpenDisplay is free as in speech and free as in beer.
• No DRM, no telemetry. The streaming is straightforward, the source is auditable, and there’s no third-party service in the loop.

For users with an older iPad who’s tired of seeing it collect dust, OpenDisplay is a practical way to put it back to work.

Practical Trade-Offs

A few honest constraints:

• Latency is real. H.264 hardware encoding is fast but not free. There is a small but noticeable lag versus a wired display, especially over WiFi. Acceptable for static content (docs, Slack, terminals); noticeable for fast mouse-driven work.
• Resolution and refresh are bounded. Maximum resolution and refresh rate depend on the hardware and the transport. Don’t expect the same flexibility as a high-end external monitor.
• macOS-only. OpenDisplay is a Mac-to-iOS solution. It doesn’t help with Windows or Linux as the host.
• Limited support channel. As a small open-source project, support is community-driven. If you hit an edge case, the issue tracker is your support desk.
• Battery impact on the iPad. Streaming a Retina display over WiFi is a real battery draw. Plan accordingly for long sessions.

These are honest constraints of the underlying technology, not flaws in the implementation. For the use case it’s designed for, OpenDisplay works well.

Who Should Care

OpenDisplay is a good fit for:

• Mac users with an older iPad that Apple no longer supports with Sidecar.
• Developers and writers who want a second display without buying additional hardware.
• Privacy-conscious users who prefer auditable, local streaming over cloud-based alternatives.
• Travelers and remote workers who already carry an iPad and want to use it productively on the road.
• Tinkerers who want a clean Swift reference implementation for display streaming and virtual display APIs.

If you need absolute-zero latency for gaming or color-accurate work, a wired external monitor remains the right answer. If you need a flexible second display on a budget, OpenDisplay is a serious option.

Summary

OpenDisplay is a focused, well-scoped open-source Sidecar/Duet alternative. The Swift codebase, hardware H.264 encoding, Retina HiDPI support, and touch passthrough cover the features that actually matter for daily use. The GPL-3.0 license and small surface area make it approachable for users who want to understand and adapt the tool.