VYM is an application available for Linux that shows "mind maps". There are several programs that do this on the market already, but they often cost a lot of money. VYM is totally free.

You could use VYM to hash out the details of a new application, a database structure, or the organization of a website. I think I’ll find it pretty useful in developing ModCMS.

You can even export the mind map to XHTML. Sorta useful if you would like to use it for an interesting navigational system like the VYM website did.

Update: If you don’t like VYM, you can find many other mind-mapping applications at mind-mapping.org