swellweb/targetbridge

TargetBridge is a free open source tool that lets you use an older Intel iMac as an external monitor for a newer Apple Silicon MacBook, connected directly through a Thunderbolt cable. Apple removed this feature, called Target Display Mode, when it moved to Apple Silicon chips, and this project brings a similar capability back using software instead of built in hardware support. The tool is written in Swift and works as two separate small apps. One app, the sender, runs on the Apple Silicon MacBook and streams its screen. The other app, the receiver, runs on the older Intel iMac and displays that stream, showing the picture at up to 5K resolution over the Thunderbolt connection. The receiver needs macOS 14 Sonoma if you use the ready made download, owners of older macOS versions on the iMac can instead build the receiver themselves directly on the iMac, which the README says takes about two minutes. To use it, you need an Apple Silicon MacBook, M1 or later, as the sender, an Intel iMac from 2017 or later as the receiver, and a Thunderbolt 3 or 4 cable connecting them. After installing both apps and granting screen recording permission on first launch, users can choose between two stream quality profiles: a standard 2560 by 1440 mode built for low latency and stability, or a sharper 5K mode that uses more processing power. The project ships ready to use pre built apps so people do not need Xcode installed to try it, and it includes quick start guides in both English and Italian. It is aimed at people who own an older Intel iMac and want to repurpose it as a second screen instead of buying a new monitor, without needing any special adapter or dongle.