Answer by surfasb for How do I do a PowerPoint presentation without PowerPoint available?

You can use Windows Live Webapps.

You can also use the Broadcast feature which allows all your users to watch the same slideshow.

http://office.microsoft.com/en-us/web-apps-help/about-the-broadcast-slide-show-feature-HA010383019.aspx?CTT=5&origin=HA010378340

You send a link to your users and they can all watch your slideshow. You can control which slide they see from inside Powerpoint.