Checkvist helps you create and share online outlines, project plans, online checklists, and task lists.

Evernote is a note taking application which keeps the notes taken in sync across all platforms using its cloud infrastructure.

OmniOutliner is a commercial outlining software for Mac OS X.

ResophNotes is a fast note writing tool and a Simplenote client on Windows.

UV Outliner is a single pane outliner with multicolumn support.

CherryTree is an hierarchical note taking application, featuring rich text and syntax highlighting, storing data in a single xml or sqlite file.

Moo.do brings all of your tasks together into one consistent interface.

Org-mode is an Emacs Mode for Notes, Planning, and Authoring.

TaskPaper is a plain text to-do list that's surprisingly adept.

WorkFlowy is an organizational tool that makes life easier. It's a surprisingly powerful way to take notes, make lists, collaborate, brainstorm, plan.