Google Inc. said on Wednesday it had created Web software that runs both online, and offline, marking a sea change for the Internet industry by letting users work on planes, trains, spotty connections and even in the most remote locations.

The technology, called Google Gears, would allow users of computers, phones and other devices to manipulate Web services like e-mail, online calendars or news readers whether online, intermittently connected to the Web or completely offline.

By bridging the gulf between new Web services and the older world of desktop software, where any data changes are stored locally on users' machines, Google is pushing the Web into whole new spheres of activity and posing a challenge to rival Microsoft Corp., leader in the desktop software era.

"The Web is great but it doesn't work very well when you don't have a Web connection," Jeff Huber, Google's vice president of engineering, said in an interview. "Gears addresses a functional gap on the Web."

Google plans to make the Gears technology available for free as "open source" software, meaning other developers are free to use and enhance the software in their own products.

Gears promises to expand the usage of scores of Google products and services, as well as thousands of programs from independent software makers, by making them more accessible at previously inconvenient times and places.

The technology also allows developers to build Internet search and indexing of Web pages into their own software applications, Huber said.

Many such products will be able to make limited searches offline, since they will have downloaded data automatically when connected. Google's full Web search functions would return once the user reconnects to the Internet.

Early partners who will use Gears in their products include design software leader Adobe Systems Inc., maker of Flash animation and Acrobat document-sharing software, as well as new Apollo tools that work online and offline, Adobe said.

Other organizations working with Google are Norway's Opera Software ASA, maker of a Web browser popular with mobile phone users, and Mozilla, the group behind Firefox, the biggest alternative to Microsoft's Internet Explorer browser, according to Google.