MacTap is a free, open-source macOS menu bar app that turns knocks on your MacBook chassis into shortcuts. One, two, or three knocks copy, paste, accept an AI suggestion, take a screenshot, control media, or anything you map. It reads the accelerometer inside the unibody (the same sensor that detects if your laptop is falling) and classifies knocks on-device. Nothing gets uploaded, no account, no network calls. Just a small native Swift app sitting in your menu bar.