Boostnote - Boostnote is an open-source note-taking app.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
SSuite Sticky To Do - SSuite's Sticky To Do app gives you an easy way to track your tasks and organize your day.
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.
Taskwarrior - Taskwarrior is an ambitious project bringing sophisticated capabilities to a simple and elegant...
Remember The Milk - Remember The Milk is a task and time management application for mobile devices.