Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Todo by Appigo - What sets Todo Cloud apart from your run-of-the-mill to-do and task-list apps is that it is straight-up powerful. It's time to get things done.
doo - A smart, simple app for reminders and to-dos
Laverna - Laverna is a JavaScript note taking application with Markdown editor and encryption support.
Simplenote - The simplest way to keep notes. Light, clean, and free. Simplenote is now available for iOS, Android, Mac, and the web.
Notezilla - Colorful & powerful sticky notes app for Windows & Phones.