D-Day is a free Android lifestyle app developed by 한울 LAB that calculates and displays a widget for D-Day. The app allows users to easily add schedules by clicking the Add button. The widget is updated automatically, but it might not work on some Android versions and models. The app also offers a 4x1 widget that can be used for displaying D-Day.

It is a simple app that does not collect any personal information. However, the app's description and interface have some English translation errors, which might make it difficult to use for non-Korean speakers.

Overall, D-Day is a useful app for those who want to keep track of important dates and events. The app's simple interface and easy-to-use features make it a good choice for anyone who needs a widget to display D-Day on their Android device.