One of the things almost everyone has to do sooner or later is make presentations. And while some people can just stand up for a few minutes and hold an audience's attention, most of us need some sort of visual aids.
Personally, good old fashioned overhead foils work fine. But we're in the 21st century, and it's almost impossible to find an overhead projector.
So the general solution appears to be powerpoint or something similar. I've been using StarOffice Impress for a few years now. It sort of works, but it's a very clunky way of doing things.
Yesterday I came across Eric Meyer's S5, a simple but phenomenally powerful slide show system. Using a combination of XHTML and CSS you can easily and quickly put a simple presentation together. If you can edit basic html, you can put together a presentation. (And using superior content creation tools like emacs or vi, at that.)
As a very trivial example, I've put together a presentation on JKstat.