Adobe has just released a preview of a new web service called Acrobat.com Presentations. This is a tool that lets you create and edit Powerpoint-style presentations with just an Adobe ID (free), a web browser and the Adobe Flash Player.
Acrobat.com Presentations is all about creating presentations collaboratively. The nature of presentations is that often they are often authored and reviewed by a group. Acrobat.com Presentations makes it easy to give others access to a presentation as either a viewer or co-author.
Currently in a "preview release," the program is already pretty full-featured. It does much of what PowerPoint does, and does some things better. When a presentation is complete, it can be web-shared with others, or saved as an Acrobat PDF file and used for off-line presentations.
Noticeably missing, as of this writing, are support for transitions and animation. You are also limited to using the fonts provided in the application, there is no access to fonts on your system. You can't import or export to/from PowerPoint format.
(If you haven't yet tried Acrobat.com, you need to check it out. It's a free service that gives you 5 gb of free storage space, makes it easy to share your stored files with others, allows you to share your screen with others and hold web meetings, and lets you collaborate on documents with the Buzzword word processor.)