Twine

Twine is an open-source tool for telling interactive, nonlinear stories.

Graphviz

Markdown is allowed here. The short description describes the project briefly, it should not be longer than one or two sentences.

Freeplane

Freeplane is a free and open source software application for bulding mind maps.

Dita

Dia is a program to draw structured diagrams.

FreeMind2

FreeMind is a premier free mind-mapping software written in Java. A mind map is a diagram used to visually organize information. A mind map is hierarchical and shows relationships among pieces of the whole.