Tomboy is a desktop note-taking application for Linux and Unix. Simple
and easy to use, but with potential to help you organize the ideas and
information you deal with every day.

The key to Tomboy's usefulness lies in the ability to relate notes and
ideas together. Using a  WikiWiki-like linking system, organizing ideas
is as simple as typing a name. Branching an idea off is easy as pressing
the Link button. And links between your ideas won't break, even when
renaming and reorganizing them.

WWW: http://www.beatniksoftware.com/tomboy/