What are some alternatives?
Wunderlist - Wunderlist is the easiest way to get stuff done. Whether you’re planning a holiday, sharing a shopping list with a partner or managing multiple work projects, Wunderlist is here to help you tick off all your personal and professional to-dos.
Pocket Informant - Pocket Informant is the Best Calendar app for mac and iOS. Pocket Informant for iOS, Mac desktop, and Android.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Tika - Unified calendar, meeting notes editor and task manager
Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
MyLifeOrganized - MyLifeOrganized: The Most Flexible Task Management Tool.