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
Purp - A smart to-do list and goal tracker app
Simplenote - The simplest way to keep notes. Light, clean, and free. Simplenote is now available for iOS, Android, Mac, and the web.
Gone - An ephemeral to-do list
Laverna - Laverna is a JavaScript note taking application with Markdown editor and encryption support.