OpenDisplay is a free, open-source way to use an iPhone, iPad, or spare Mac as a true second monitor for a Mac. It creates a virtual display that macOS treats as an extended desktop rather than merely mirroring the main screen. Video is captured and hardware-encoded as low-latency H.264 before being streamed to the receiver. Connections can run over USB for minimal latency or Wi-Fi with Bonjour-based discovery. Retina and HiDPI output preserve sharp text, while touch gestures provide clicking, dragging, and scrolling from the receiving device. The display can rotate between portrait and landscape and rebuild at native resolution. ...