Credit: Illustration by Marc Rosenthal

As you read this, countless programmers worldwide are collaborating to write, refine, and debug open-source software. Open-source pioneer Richard ­Stallman estimates that a million programmers now contribute to these efforts, in which the original written form of the code--the source--is made freely available for everyone to work on and worry over. Once a fringe phenomenon, the practice has grown into a major force in software development.

Select from the choices above to read the entire article.