Google plans to add a presentations application to its Web applications suite on Tuesday, delivering on a promise made in April. The suite, until now known as Docs & Spreadsheets, will also be renamed Google Docs on Monday.

Because Google Docs is part of the broader Google Apps suite of collaboration and communication applications, Google Apps users will also get the presentations application.

The delivery of the presentations application will no doubt once again turn up the heat on industry discussions that Google Docs and Google Apps rival Microsoft's Office suite of productivity applications and the Outlook/Exchange messaging platform.

There is a key architectural difference between the Google and Microsoft suites: Google's is hosted in the search company's data centers while Microsoft's is packaged software designed to be installed on users' computers.

The viability of Web hosted applications, with their software-as-a-service (SAAS) model, is no longer in question, although the consensus is that, while the future belongs to them, they will not completely displace traditional packaged applications.

The issue is that, while Google and others like Zoho and Zimbra push ahead expanding and improving their SAAS suites, Microsoft is perceived by many to be dragging its feet in coming up with SAAS versions of its Office products.

"Microsoft needs to take a careful look at its enterprise strategy for both messaging and the desktop," said Rebecca Wettemann, an analyst with Nucleus Research.

Having delivered the presentations application, Google Docs and the broader Google Apps, which includes e-mail, instant messaging, calendar and a Web page creator, have filled the only big hole they had in their ability to compete with Microsoft Office and Outlook/Exchange, she said.

"Microsoft should be very concerned," Wettemann said.

The benefits of SAAS communication and collaboration suites have already caught the attention of thousands of organizations of all sizes worldwide.

Because the vendor -- Google in this case -- hosts the software, which end users access via a Web browser, clients don't have to install the software or worry about upgrading it. Another benefit is that this type of SAAS application, designed to live on a hosted server is typically built to make it easy for users to share documents and collaborate on them.

There are downsides to the SAAS model as well. Security concerns exist about housing applications and data in a vendor servers. Availability and performance problems sometimes arise from server failures.