Jreepad

Jreepad allows you to store and edit all your little nuggets of text in an incredibly intuitive tree structure. Each "node" on the tree has a plain-text "article" associated with it, meaning that a Jreepad file becomes almost a freeform database, storing all kinds of information.

Write to-do lists, plan the structure of your book, keep a library of code snippets... people use it for all sorts.

Verison 1.5::

JTextile formatting, for a convenient and elegant wiki-like formatting of text

Infinite undo/redo of changes to text in nodes

Document icons and file associations (under Mac OSX) for added convenience

Improved keyboard shortcuts

A handful of bugfixes

Requirements

Java 1.4 or later