Google Calendar - Spend less time managing your day & more time enjoying it
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Business Calendar - Powerful and easy to use calendar app for Android including weather, widgets and tasks.
Todo.txt - Track your tasks and projects in a plain text file, todo.txt. A todo.
Jorte - Schedule books must be practical and has a good design.
EssentialPIM - EssentialPIM is a free Personal Information Manager that keeps up with the times and lets you manage appointments, tasks, notes, contacts, password entries and email messages across multiple devices and cloud applications.