OpenDisplay

Turn your spare Apple devices into second monitors for your Mac — free, open source, no subscription.

iPhone, iPad, and spare Macs. A self-hosted alternative to Apple Sidecar, Duet Display, and Luna Display: true extended display (not just mirroring), Retina-sharp, over USB or WiFi, with touch and scroll input.

Why OpenDisplay exists

Turning an iPhone or iPad into an external display for a Mac is a solved problem — but every existing option has a catch:

• Apple Sidecar is free but requires both devices on the same Apple ID,

doesn't support iPhones at all, and only works on supported hardware pairs.

• Duet Display moved to a subscription.
• Luna Display requires a hardware dongle.

OpenDisplay is the missing option: a free, open-source, no-account, no-dongle way to use the iOS device you already own as a true second display. If you were about to write your own — don't! Contribute here instead; the hard parts (virtual display creation, low-latency H.264 pipeline, USB transport, input injection) are already working.

Features

• True display extension — macOS treats the device as a real second

monitor (drag windows to it, arrange it in System Settings), not a mirror. Mirroring is also available as a mode.

• USB-wired for lowest latency — streams over the Lightning/USB-C

cable via macOS's built-in usbmuxd; plug in and go, no network, no WiFi jitter, no helper tools.

• WiFi with zero config — the iPhone advertises itself via Bonjour;

pick it from a dropdown on the Mac.

• Retina / HiDPI — the virtual display matches the device panel

pixel-for-pixel (@2x), so text is sharp.

• Touch input built in — your iPhone becomes a touchscreen for macOS:

tap to click, drag to drag, and two-finger scroll that feels like a trackpad. (Apple Pencil support is on the roadmap.)

• Portrait or landscape — rotate the device and the virtual display

rebuilds itself as a vertical monitor at native resolution.

• Low-latency pipeline — hardware H.264 or HEVC encode (VideoToolbox,

real-time mode, no B-frames), TCP_NODELAY, frame-drop backpressure with keyframe recovery, decode-and-render via AVSampleBufferDisplayLayer.

• A spare Mac as a display — install the small *OpenDisplay

Receiver* app (macOS 12+) on an old Mac and any other Mac extends onto it over WiFi or a Thunderbolt/Ethernet cable, at native Retina resolution.

• Self-hosted & private — your screen never touches anyone's server.

Two small apps, one TCP connection, that's it.