FreeMind is an open source mind-mapping program, written in Java:
http://freemind.sourceforge.net/wiki/index.php/Main_Page
Another wiki, WikkiWiki, provides integration of FreeMind maps:
http://wikka.jsnx.com/FreeMind
Here's a nice example of it in use (Java needed):
http://wikka.jsnx.com/MindMapRecentChanges
This feature would be ncied to have in DokuWiki at some point.
Thanks,
Ben