Will it always be a Microsoft Windows world? That's what I hoped to find out when I sliced open the box containing the new PC I'd ordered from WalMart.com. It had a respectable 1.6-gigahertz processor, a serviceable 40-gigabyte hard drive, a CD-ROM drive, an MP3 player, and enough other software to keep me occupied for life, though supporting it all was a barely adequate 128 megabytes of RAM. Okay, I knew this chunky black box wouldn't be the sexiest PC on my block. But that was fine, considering its paltry $278 price tag -- and that I'd really ordered it for what it didn't have: any Microsoft software whatsoever. Rather than Windows and Office, it came with Linspire 4.5, one of the many commercial versions of the open-source Linux operating system that are now available, and a link to a website where I could download a variety of open-source applications. n When I plugged in my Wal-Mart machine and hit the power button, I got a look at an alternate future that ought to be fueling Pepcid sales among Microsoft executives. The computer featured a glamorous new desktop screen and sophisticated control panels, help menus, and audio tutorials. I was instantly able to connect the machine to the Internet, where I downloaded -- free of charge -- open-source equivalents of the Microsoft Office programs I use every day: Word, Excel, PowerPoint, and Internet Explorer. The free software may not have all of Office's bells and whistles, but the version of it I chose, Open Office, does everything I need it to do -- including saving files in Word format.

The back-office world of servers and databases is no longer Linux's most exciting frontier. Sure, Linux has gained an irreversible hold in behind-the-scenes corporate computing centers, where some 67 percent of corporate Web servers are Linux machines running open-source software. Companies from Schwab and Merrill Lynch to L. L. Bean and Pep Boys have converted parts of their back-office operations to Linux, and IBM, Oracle, and other companies are spending millions to make their own business software run on the operating system. But over the last three years or so, the capabilities of open-source software have finally caught up with those of Microsoft applications in the space where most human-computer interaction actually occurs: the desktop. "For the user who spends 50 percent of the time in the Web browser and another 40 percent in the mail client, the Linux desktop is already there," says Andy Hertzfeld, an open-source programmer famed for his work on the original Apple Macintosh operating system.