Gone - An ephemeral to-do list
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
Check - Check is a unit testing framework for C, which runs on environments such as GNU/Linux, GNU/Hurd, BSD, and Mac OSX.
Simplenote - The simplest way to keep notes. Light, clean, and free. Simplenote is now available for iOS, Android, Mac, and the web.
Things - Things is an easy to use task manager.