Prezi. Its worth a play, not only because it's such an 'outside-the-box' take on presentations, but also because of the way they've innovated the user interface and handled user training. Most applications take well understood user interaction standards and put them together in new ways or for new purposes. This keeps things usable. Now and then, a piece of software changes things so drastically, that it has to invent ways for users to do things simply (think back to that first day you rubbed the click wheel on an iPod). It's always risky, but when its done well, it sets a new standard. Specifically, Prezi is placed to standardize zooming as a way of representing nested hierarchies in the user psyche.
Prezi introduces some all-new interface tools in order to bring a new kind of zoom-happy 'slide' presentation to the masses. But what's also a great lesson for us to take home as education designers, is the way they integrate user training. There's a great risk users will sign up, get started and give up after about 60 seconds because they can't figure out how to handle this brand new thing. Prezi manages to work in multiple ways for the user to learn the program basics without throwing up roadblocks or becoming a nuisance. It's also presented in a friendly way, that is, pretty pictures, plenty of whitespace, large text and handwriting fonts. The visual design makes it look like it's going to be easy (see "Don't just make it easy, make it look easy") which contributes to overall usability and the likelihood of large scale adoption. Check it out.