the Simple Standards-based Slide Show System (S5) gives you PowerPoint-like presentations in pure XHTML, CSS and JavaScript. See it in action here. Released under the Creative Commons Attribution-Sharealike 2.0 license, and backwards-compatible with OperaShow Format 1.0 — Neat!
I’m not giving up using Keynote, but it sounds perfect for retro-folk who still like writing your slides in Emacs or Vi…