OmniOutliner - OmniOutliner is a writing app for collecting information, outlining ideas, adding structure to any sort of writing.

Todoist - Todoist is a to-do list that helps you get organized, at work and in life.

Dynalist - Dynalist is a web app that lets you break down and organize your thoughts in the format of lists.

Todo.txt - Track your tasks and projects in a plain text file, todo.txt. A todo.

Workflowy - A better way to organize your mind.

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.