Impressive
http://impressive.sourceforge.net
"Impressive is a program that displays presentation slides. But unlike OpenOffice.org Impress or other similar applications, it does so with style. Smooth alpha-blended slide transitions are provided for the sake of eye candy, but in addition to this, Impressive offers some unique tools that are really useful for presentations. "
Robert's talk - Proudly presenting AJAX-S!
http://www.robertnyman.com/2005/11/13/proudly-presenting-ajax-s
"I've been thinking about creating an AJAX-based slideshow for a while, and today it happened!"
MagicPoint is a presentation tool for X11
http://www.mew.org/mgp
(but, does it make you dumb like PowerPoint?)