Program: TiddlyWiki
License: BSD OpenSourceLicense
Description: A personal wiki or Content Management System, stored as a single html-file. Very expandable with a multitude of plugins (under the same license) and adaptations. Use on all major systems/browsers.
Website: http://www.tiddlywiki.com/
Other: Mature software with highly active user community (e.g http://groups.google.com/group/tiddlywiki/) and developers community.
Extremely versatile, can be used for e.g;
http://www.tiddlywiki.com/#Examples