Acta
An original outlining software written in 1993 for Macintosh computers, now available for free download (Mac only). The site provides interesting background on the program and its uses.
Idea Cruncher
A simple program for Microsoft Windows that helps you organize ideas. Good for writing, brainstorming, to-do lists, outlines and other planning tasks.
MacFlow/WinFlow
Extremely adaptable and intuitive flowcharting program. Lets you import an existing outline from text directly into diagram mode. Allows for "nested" diagrams, i.e., placing shapes within shapes. Free trial download available.