What are some alternatives?
When comparing Org mode and OneNote, you can also consider the following products
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Evernote - Bring your life's work together in one digital workspace. Evernote is the place to collect inspirational ideas, write meaningful words, and move your important projects forward.
Remember The Milk - Remember The Milk is a task and time management application for mobile devices.
Google Keep - Capture notes, share them with others, and access them from your computer, phone or tablet. Free with a Google account.
WorkFlowy - WorkFlowy is an organizational tool that makes life easier. It's a surprisingly powerful way to take notes, make lists, collaborate, brainstorm, plan and generally organize your brain.
Simplenote - The simplest way to keep notes. Light, clean, and free. Simplenote is now available for iOS, Android, Mac, and the web.