CIOs would care a lot less about open source software if they didn\u2019t see it as a possible solution to the problem that has plagued them for decades: A lack of standards in the IT infrastructure.If there is an open source killer app, it\u2019s the GNU General Public License (GPL). This is the controversial Magna Carta of the movement, developed by Richard Stallman in t he 1980s to ensure that if someone took the software he wrote and distributed for free and tried to modify and sell it, he and the rest of the world would get a chance to see exactly what they had done?i.e., the new source code. Stallman\u2019s rules have nothing to with money. Anyone who creates new software can charge whatever he wants. But the rules ensure that the code is shared, and that has turned out to be a powerful weapon for promoting consistent, standard versions of the software it governs, like Linux, which Stallman refers to as free software. "Increasingly, the developers of non-free software use it to control the users," he says. "Only free software puts you in control."CIOs who are contemplating using open source software should understand the licenses behind the applications they are using, so they understand what they can and cannot do with the code.The GPL is as controversial in the open source community as Stallman himself, who is uncompromising and temperamental. (He can\u2019t, for example, abide the term open source.) "A lot of people say they dislike the GPL when really they just dislike Richard Stallman," laughs Jeremy Allison, who developed Samba, an open source file and print server licensed under the GPL. "It is absolutely a landmark document. When historians look back at the history of software, they?ll see it as a turning point," he says. "It levels the playing field. It means you can\u2019t take the software and make it proprietary and closed."Critics say the GPL has never been tested in court (and probably wouldn\u2019t hold up if it were). Larry Rosen, general counsel for the nonprofit Open Source Initiative, says that\u2019s a testament to the power of the GPL. He has seen violations and threats of litigation, but the disputes always get resolved out of court. "What company wants to be seen as the villain for stealing something that\u2019s free?" he asks rhetorically. "Nobody. It would be a public relations disaster."Allison says the GPL has protected Samba from being appropriated by proprietary vendors, but he won\u2019t offer specifics. "These are smoke-filled-room discussions," he says.The GPL and the code of conduct that it established are the only reasons that commercial versions of Linux have not gone the way of UNIX, which was developed as a standard, free operating system by AT&T in the 1960s but eventually "forked" into many incompatible versions when hardware vendors changed the code to optimize it on their machines. Two different versions of Linux have already emerged at the server and desktop levels, one from RedHat, dominant in the United States, and another from United Linux, an alliance of smaller vendors led by Germany\u2019s SuSe, which dominates the Linux market in Europe. The GPL ensures that the core Linux code inside the two versions works the same way. Still, the different vendors do their damnedest to tweak their versions so they look and act differently in subtle ways. The two sides show no sign of aligning anytime soon. Asked about the split, Matthew Szulik, RedHat\u2019s CEO, evades the question. "We believe in choice," he responds.CIOs are already frustrated by what they see as d\u017dj\u02c6 vu all over again with Linux distributors. Even subtle differences matter when you\u2019re trying to roll out software across hundreds of servers and thousands of desktops and train IT staff and users on a new system. "There is no standard," worries Larry Shutzberg, CIO of RockTenn, an Easley, S.C.-based packaging manufacturer. "You need a single, standard version to go against Microsoft."