TreeSheets is an open-source "Free Form Data Organizer" for Windows, Mac, and Linux. It's an outliner! It's a spreadsheet! It's a mind-mapping tool!
THE FULLER MAP This document is a study of the comprehensive designer Buckminster Fuller, an outstanding character of the 20th century, and a kind of practical visionary. [...] This presentation of his ideas is not intended as a slavish devotional exercise, nor a piece of cynical criticism. Part of the plan here is to investigate the logic of synergetics. At this stage the account is verbal, not visual, but what is important in geometry is the logic rather than the pictures. The text is a work-in-progress, begun in August 1991, and originally written to meet the structural requirements of John Wood's IDEAbase system. It was compiled and edited as an experimental, dynamic, interactive, screen-based document. It was not, therefore, intended as a completed linear text to be printed onto paper or other static medium.
The Intor.net - A userless, interfaceless website and mindmap generator that creates interesting things from URLs. [via mefi projects]
The Visual Understanding Environment (VUE) is a free, open source program developed at Tufts University. It lets you create concept (mind) maps and analyze them in various ways. One very useful thing it can do is generate concept maps from .CSV files. Here’s an introductory screencast (length: 6 min 9 sec). You can watch all related videos here. The program runs on Windows, Mac, and Linux.