Maybe the standard mind mapping tools with a bit navigation can help here, too. Not as cool in presentation, but useful anyway. Xmind and FreeMind are free desktop tools.

Maybe not as comfortable but pretty flexible with quality voices from the reasearch community and totally free is MaryTTS:

Online Demo

Download

It is based on Java. So, you need a Java runtime on your machine. The installation is done on the command line in the folder of the download by:

java -jar mary-standalone-install-3.6.0.jar

The installer allows to install additional voices for different languages on demand during installation.

This stuff is a real client-server solution. So, you have to start the server process before the client is started. But, this also allows to use it in a Web environment to create audio files on demand. I use it to create cost-free commercially usable TTS audio files for projects like this:

Snowman Joe (Details how to create this)

But, not all voices are allowed to use for this in the MaryTTS package. Have a look at the copyright notes for details.

I found the Stephen King posting here and thought maybe you're also interested in some free Halloween stuff:

*Applications: Jigsaws, Screensavers, Horrible Adventcalendars (for those who also like Xmas)
* Desktop: Wallpapers
* PDF prints: Greeting Cards, Posters, Painting Book

Jigetiser Halloween Lovers