If I had to levy one complaint at PowerPoint, it would be that its presentations are too linear. You can only advance one slide at a time, and there's no way to arbitrarily pan around or zoom in on details within a single slide. A free PowerPoint add-in solves those problems handily.
pptPlex is a PowerPoint add-in that lets you create non-sequential, zoom-able presentations using your existing PowerPoint deck. It's a product of Microsoft Office Labs that addresses some key shortcomings in the static, linear nature of everyone's favorite presentation tool.
The add-in gives you a number of dynamic templates which you can use to reorganize your presentation. For example, you can group related slides into sections, and then, during the presentation, zoom "out" to view the entire group, make a slide selection, and then dive deep back to your selected slide.
pptPlex also gives you deep zoom -- if you have a lot of details in a slide, you can zoom in for a closer look. This is great for "quad slides" (those monstrosities which pack four graphs onto a single slide in a misguided effort to show fewer slides without reducing any of the actual information) and for showing detail in a high resolution photo.
If all this sounds familiar, it's because this is not entirely unlike Prezi, a Web-based presentation tool that we heartily endorse as well.