A long-standing accessibility feature where physically shaking the device prompts a pop-up to undo or redo your last action, such as typing or deleting an email.

Shaking your phone while the app is open captures a screenshot and opens a feedback menu to report issues.

Apps like WeChat and Line have used a "Shake" feature to help users find nearby people or add friends by shaking their phones simultaneously. 💻 Windows PCs 1. How do I enable/disable Shake? - WeChat Help Center

Popular on Android (especially Motorola "Moto Actions"), this allows you to toggle the flashlight on or off with two quick "chopping" motions.