pptPlex, a Microsoft Labs-created add-in for PowerPoint that makes presentations more interactive, hasn't seen a lot of development since it appeared back in 2008. A new update gets the add-in working for users of the forthcoming Office 2010 release.
Aside from the compatibility fixes (and the removal of the feature to add sections to presentations, since that's now a native PowerPoint feature), the biggest change in the latest version is support for the multi-touch features added to Windows 7. If you're presenting on a multi-touch device, you can move between slides by swiping, and zoom by pinching. pptPlex is a free add-on for Office on Windows.