Android: CalendarNotify's particular take on mobile calendaring lies in the variety of ways it can show you a calendar notification.
Specifically, it offers calendar notifications within the notification drawer and on the lock screen if you're running Android Lollipop, with a customisable display and a choice of layout styles. That's a very specific niche within calendar apps, and as such it's going to be a good match if you're a fan of the widget style to keep your appointments running on track.
If you're in the market for a full-featured Android calendar app, you could also consider Lifehacker favourite Business Calendar.
Calendar Notify Agenda Status (free) [Google Play]