UpNote - A beautiful and clean cross-platform app for notes organizer
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Notesnook - Notesnook is a simple and private note taking app that keeps your notes organized and synced on your phone, tablet and computer.
Todo.txt - Track your tasks and projects in a plain text file, todo.txt. A todo.
todoZero - A powerful to-do and note app for busy people.
EssentialPIM - EssentialPIM is a free Personal Information Manager that keeps up with the times and lets you manage appointments, tasks, notes, contacts, password entries and email messages across multiple devices and cloud applications.