Telegram - Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free.
Google Calendar - Spend less time managing your day & more time enjoying it
Revealit.me - ReveaiIt.me allows you to send a one time link to a self-destructing document.
CalenGoo - Features | 1.0.175 for Android™
FCorp My Calendar - Manage diary/note, schedule, todo, birthday, etc.
Jorte - Schedule books must be practical and has a good design.