Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Taskful - Deadlines, meet your match.
GoodTask - Task manager based on iOS reminders and calendars
Calendarist - Time blocking companion for Google Calendar
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.
Centered - Centered helps you get into a Flow State faster and stay there longer so you can do your best work.