In its latest challenge to Microsoft’s desktop-based productivity software, Google yesterday launched a public beta version of the long-rumored Google Calendar tool, which allows users to create and track appointments through a Web-based interface accessible from any computer connected to the Internet.

Like most beta products at Google, the calendar was rolled out without hoopla, but is already generating interest – and praise – among Web users worldwide, including thousands of bloggers. “My first impression: It’s fast, slick, and stable,” writes Michael Arrington, publisher of the widely followed product review blog TechCrunch.

The reason: Google remains true to its tradition of building interfaces that echo but simplify tasks historically done using desktop software such as Microsoft Outlook. As with Gmail, Google’s Web-based e-mail manager, Google Calendar runs entirely inside a browser program such as Microsoft Internet Explorer or Mozilla Firefox. It takes advantage of a programming approach called AJAX (Asynchronous JavaScript and XML) to reproduce the look and feel of desktop software over the Web – while adding features of Google’s own invention, such as the ability to transfer events mentioned in Gmail e-mails directly to the calendar.

“Calendaring is one of those problems where we felt like it hadn’t been done right before, and we felt we could add some value to it,” says Carl Sjogreen, Google’s product manager for the calendar project. “We really set out to make a calendar program that made it drop-dead simple to get information onto your calendar. With one easy graphical click-and-type interface, you can enter data, and we have some pretty sophisticated natural language processing technology that lets you type in a description of an event – like ‘Meet Bob for coffee Thursday at 7 p.m.’ – and add it to your calendar without filling in a big form.”

That’s in stark contrast to Outlook’s calendar, which requires users who are creating calendar entries to fill in a minimum of three separate boxes: one for the subject, a second for the start time, and a third for the end time.

Google Calendar is not the first Web-based calendar to emerge in recent months; its features are largely matched by existing calendar services, such as Kiko and 30 Boxes, and it joins a raft of other free tools for personal organization and time management, such as Upcoming, Gootodo, and GTDTiddlyWiki (a note-taking program customized for followers of David Allen’s Getting Things Done). And it’s just one advance in the larger Web 2.0 movement, a flowering of free online tools for creating, organizing, and sharing personal information (see “Web 2.0’s Startup Fever”).

But because of Google’s prominence, wealth, and well-known ambition to organize all the world’s information, its move into calendar software underscores the tectonic shifts underway in the market for home and office software – from standalone desktop applications to more easily accessible Web-based applications, and from complex, feature-laden programs written over the course of years by huge development teams to simpler tools created by small, agile teams using standardized approaches like AJAX.

Google’s recent purchase of Upstartle, creator of a free online word processing service called Writely, is another clue to the company’s intentions. “The current suite of office tools, Word and Outlook chief among them, are simply too hard to use,” says Mark Hurst, author of Gootodo and founder of Creative Good, a New York-based consulting firm that specializes in user interface design. “Microsoft has been promising for about 10 years that a big improvement is just around the corner, and it has never come. Google is in a position to fix that for a lot of users.”

Of course, methods like AJAX are available to all Web developers, meaning Google won’t have the market for online productivity applications to itself. “Applications written on AJAX are making it a lot easier for people to write competitive and compelling Web applications that have all the functionality of, and in some cases more than, the desktop applications,” says Kiko’s co-founder Justin Kan.

And Microsoft isn’t likely to be left behind in the new competition. While the company has no plans to chuck its lucrative desktop software business, it’s already building Web 2.0 standards such as RSS feeds (a way to subscribe to recently published information on the Web) into the next-generation Vista operating system, and is gradually unveiling its own set of Web-based tools at www.live.com to enhance its desktop productivity software.

But there are no signs yet that Microsoft is fundamentally reinventing its tools for tracking appointments and tasks – which is what many developers of Web-based time management tools believe they are doing.

“I think we are going to see calendars as a place to aggregate a lot more data in the future,” says Kan. “For example, I put an RSS feed from Upcoming.org into my Kiko calendar. It displays events in Cambridge, directly in my calendar. I found an event that I think I am going to tonight – it’s not something I had looked for, and would never have known about otherwise.”

Hurst of Creative Good agrees that Google Calendar, Kiko, and similar programs offer big improvements over earlier generations of calendar software – but he argues that even Google hasn’t gone far enough.

“There are two kinds of improvement going on with the use of the new Web 2.0 technologies,” Hurst says. “There are the interface improvements. Google has made the interface better, and that’s a good thing. But the other kind of improvement – which is really rare – is when someone creates a tool that operates under a different philosophy.”

Hurst argues that mainstream software and Internet companies are still obsessed with finding ways to send consumers more information – for example, in the form of RSS feeds and shared calendar entries. “Most tools allow people more ways of consuming more bits. But that doesn’t make people more productive,” Hurst says.

What’s needed instead, Hurst argues, is a way to receive fewer bits. A central feature of Gootodo, for example, is the ability to transfer non-urgent tasks to the Gootodo task list at a future date by e-mail, thereby keeping the current day’s to-do list as short as possible. “If people use Google Calendar without also using a to-do list manager like Gootodo, they are at risk of being overwhelmed,” Hurst says. “Everyone’s got different needs. But there is a psychic cost to keeping bits around.”