Microsoft Corp. has defeated most competitors to its Office suite of software. But a new edition of the popular program will be challenged by free or low-cost Web-based alternatives from Google Inc., which some businesses are adopting.

Microsoft has added Web-friendly features to Office 2010, which will become offered to business starting in May, that allow people to run over the Internet Word, Excel and other applications through Web browsers and to edit documents all together with other users. The company will also offer a free, online version of Office 2010 that has advertising.

The moves are Microsoft’s most firm effort yet to refashion one of its mightiest cash cows for the era of “cloud computing,” a Google-backed trend in which applications are run in remote data centers and often rented to customers rather than purchased and installed on customers’ personal computers.

Google’s online Apps, which execute related tasks to Office, have gathered steam in recent years by reducing costs and administrative hassles. Google also competes with behind-the-scenes software in the Office family for running email systems and company Web sites, called Exchange and SharePoint.