The best replacement for reminder is remainder.

The best alternatives to reminder are rated as following:
★★★★★  remainder
★★★  reminders
★★★  reminding
★★  demandforce
★★  kind reminder
★★  shadow strike
★  gentle reminder

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Speaking about reminder, one probably shouldn't forget about snooze iphone.

Other search terms related to reminder and their ratings are:
★★★★★ snooze iphone
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