Todoist - Todoist is a to-do list that helps you get organized, at work and in life.

Toggl - Toggl is an online time tracking tool. It features 1-click time tracking and helps you see where your time goes. Free and paid versions are available.

doo - A smart, simple app for reminders and to-dos

Harvest - Simple time tracking, fast online invoicing, and powerful reporting software. Simplify employee timesheets and billing. Get started for free.

Laverna - Laverna is a JavaScript note taking application with Markdown editor and encryption support.

RescueTime - Time management software that shows you how you spend your time & provides tools to help you be more productive.