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."