TickTick - TickTickis a cross-platform to-do list app & task manager helps you to get all things done and make life well organized.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Synapbook - Synapbook is one of the powerful knowledge management tool for creating cloud-based notes in tree...
Todo.txt - Track your tasks and projects in a plain text file, todo.txt. A todo.
Taskwarrior - Taskwarrior is an ambitious project bringing sophisticated capabilities to a simple and elegant...
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.