Tokyo-based app developer Lightning LLC has released MustDo, a scheduling app for Apple iPhones, on the Apple App Store. It is a new app from the developer that made KeyAlarm, which turns calendar events into alarms.

MustDo sounds an iOS 26 AlarmKit alarm at the registered time when users enter a task and time. It is in the same category as the Clock app, so it rings full-screen even in silent or focus mode and continues until the user stops it. When the alarm is stopped, it is marked as complete. If the user has not done it yet, the user can choose one of “in 10 minutes,” “in 1 hour” or “tomorrow” to be notified again. If only a task is entered, the default is “tomorrow 9 a.m.” Repeats can be set at the level of the iOS Calendar, and there are 25 alarm sounds.

It stores tasks only in the user’s Apple iCloud without servers, and it does not require account registration. It also supports the Model Context Protocol, so if a user asks Claude AI, “Add ‘take medicine’ to MustDo,” an alarm sounds on the iPhone at the relevant time.

It can be used on iPhones running iOS 26 or later and supports eight languages, including Korean. Users can use it with a monthly or annual subscription after a 30-day free trial. A plus is that it does not automatically charge after the trial ends. Even without a subscription, already registered tasks keep ringing, and users can stop them, snooze them again or delete them. A subscription is required only to register new tasks.