Vịt Đếm Ngược is a free Android application developed by Develop Team MK in the Lifestyle category. The app helps students countdown to the National High School Exam 2021 by displaying the number of days, hours, minutes, and seconds left until the exam. It also includes a feature to update the exam date for students in grades 10, 11, and 12.

In addition to the countdown feature, the app also has a diary function to help students keep track of their memories and special moments during their final days of high school. The app also includes cute quotes, wishes, and messages to motivate students during their exam preparation. A widget on the home screen provides easy access to the app, and users can customize the app's background image, font color, and font style. The app also includes fun games such as "Who Wants to Be a Millionaire" and "Brain Teasers" to relieve stress after a long day of studying. Lastly, the app offers daily horoscope readings for each zodiac sign.