Microsoft To Do is Microsoft's task management app for lists, reminders and daily planning, and this ding is one of its familiar notification sounds for completing a task or receiving a reminder. Because the tone is short, clean and instantly recognisable to anyone who uses the app for work or study, editors have lifted it out of the phone and into short videos. There it works as shorthand for getting things done, without needing any explanation, which is why it keeps appearing in productivity edits, study vlogs and checklist-style clips.