Gone - An ephemeral to-do list
Streaks - The to-do list that helps you form good habits.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Check - Check is a unit testing framework for C, which runs on environments such as GNU/Linux, GNU/Hurd, BSD, and Mac OSX.
Taskade - Make lists, organize your thoughts, and be inspired to get things done. Taskade is a collaborative space for your tasks.
Things - Things is an easy to use task manager.