UV Outliner - UV Outliner is a small and powerful single-pane outliner.
Workflowy - A better way to organize your mind.
Remember The Milk - Remember The Milk is a task and time management application for mobile devices.
Orgzly - Outliner for notes, tasks and to-dos
Planka - Planka is an open source project management software similar to Trello.
Dynalist - Dynalist is a web app that lets you break down and organize your thoughts in the format of lists.