Dynalist - Dynalist is a web app that lets you break down and organize your thoughts in the format of lists.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Workflowy - A better way to organize your mind.
Todo.txt - Track your tasks and projects in a plain text file, todo.txt. A todo.
Indigrid - Plain text outliner with side-by-side views.
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.