"The app is called You're Cancelled" began the now-viral tweet by Mattie Kahn in 2020.
"When you've made plans and you wish you could cancel, you go into the app and press a little button. If the other person presses theirs too, congratulations! Confetti explodes and your plans are cancelled. If you press yours but the other person doesn't, your plans remain intact and they never find out you wanted to cancel."