I recently received this email:
What is the Open Source equivalent (or better) of PowerPoint? Where should someone go to download it?
Are there any difficult questions when downloading it?
If someone creates a presentation in the OS version, then takes their file to another computer, can PowerPoint play it or does the other computer need to download the OS version?
Anything else that should be thought through?
Perhaps the title Best Office/Productivity/Diagramming Software isn't sufficiently targeted at all the replacements, so let me restate that if you need a Free replacement for PowerPoint that can import/export PowerPoint files, OpenOffice.org's Impress tool works great! You can download it right on that page. It does request a donation, but you can skip that. The installation is pretty simple, though it does request that you register (free process) which helps them understand their users more. You have the option of skipping the registration.
Learning to Use Impress
There are Tutorials available online which are pretty decent. The person who wrote those is a former teacher.
Import/Export and PowerPoint compatability
While it can import/export to PowerPoint format, it doesn't do that by default. And sometimes you'll have problems with the import/export function, so it's best to get all of your friends to use OpenOffice.org as well. Unless you have some really really good reason that you use PowerPoint, OpenOffice.org is a much better piece of software that doesn't require any expensive licensing fees.
Generaly speaking, though, you can run the files that were created by OpenOffice.org on any Microsoft Office computer. Just be sure to select "Save as type" of the proper Microsoft Office program.