快记 is a free iPhone app designed for Business & Productivity. It allows users to quickly mark important events on their calendar using negative one-screen widgets. Whether it's noting workout days, overtime, leave days, or any other events, 快记 simplifies the process into just three steps. Users need to light up their phone screen, swipe left to access the negative one-screen widget page, and add the mark on the calendar widget. The app supports data backup to iCloud, adapts to Dark Mode, and is compatible with iPads in both portrait and landscape orientations.

快记's core functionality revolves around operating on the negative one-screen widget, and users are advised to refer to the app's settings page for detailed instructions on adding the widget. In case the widget fails to load, tapping on the "Unable to load" text can restore its functionality.