The Office 2.0 movement has a strong showing of free online presentation software, a few of which having enough features that they could replace PowerPoint in many offices.
Many of these office 2.0 presentation software packages are still in beta, but the good part is that most of them are free.
Zoho Show
Description: A high-end solution to office 2.0 presentation software, Zoho Show packs a punch. Featuring rich drawing capabilities and many of the same bells and whistles as its desktop competitors, Zoho Show makes a strong showing for replacing a company's conventional presentation package. Zoho Show is part of the Zoho office suite which also includes a word processor and a spreadsheet.
ThinkFree Presentations
Description: Rounding out the ThinkFree office suite is Presentations, a great online presentation software solution. Like the rest of the suite, Presentations allows users to go into it under quick edit mode of minor touch-ups or power edit mode for major designing. It features a whole host of options for creating professional presentations.
Spresent
Description: Spresent is a Flash-based Office 2.0 presentation package. It has an easy-to-use interface and offers some nice animations. There's an example library to help you get started, and you can also publish the presentation to a public folder and embed it onto your website.
Google Docs - Presentations
Description: Google's free online presentation software doesn't quite measure up to the other presentation software available online, and seems to be the weak point in the Google Docs series of office 2.0 applications. While it might be adequate for quick presentation, it stutters trying to do much more than that.
Thumbstacks
Description: This neat little Office 2.0 presentation software package isn't quite ready to stand up to the big boys, but it offers some neat features like the ability to embed Google Maps into the presentation. Once its feature set grows, it may be a nice alternative to desktop solutions or other free online presentation software.
Empressr
Description: Despite an impressive name, Empressr has a long ways to go before its ready for prime time. While it has some of the basic functionality of other free online presentation software, it lacks the richer feature set that lead someone to abandoning their current presentation solution.