Calender is fully free and user friendly application.
A simple calendar with optional CalDAV synchronization. You can easily create recurring events and setup reminders, it can also display week numbers.
This is the ScheduFlow Personal Edition calendar from Android 4.4 which was released by Google. Google's current calendar is different - better in most ways but it has stupid horizontal scrolling in the month view. ScheduFlow / schedule flow / scheduleflow calendar is loved by many Android users as it's month view is phenomenal.
Contains a monthly view and an event list widget where you can customize the color of the text, as well as the alpha and the color of the background.
Contains no ads or unnecessary permissions. It is fully opensource, provides customizable colors.
The Storage permission is needed only for exporting or importing events from .ics files.
The Contacts permission is used only at importing contact birthdays and anniversaries.