Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
doo - A smart, simple app for reminders and to-dos
Any.DO - The #1 task management app used by over 11 million people globally, Any.do is your free mobile and online task manager for Android, iPhone, Web and more.
Laverna - Laverna is a JavaScript note taking application with Markdown editor and encryption support.
Microsoft To-Do - Task management tool
Simplenote - The simplest way to keep notes. Light, clean, and free. Simplenote is now available for iOS, Android, Mac, and the web.