Open Source is another example of open and available material that presents powerful educational opportunities. It would, for example, be difficult to find a better example of authentic learning than participation in a real world project with all of it's design, organizational, and personality issues.
The immediate thoughts might that it requires a specialized computer science skill set to contribute. However, as is usually the case, reality is far more nuanced. Open source projects touch on almost every disciplin, from art to zoology. In many cases the subject matter expertis is sufficient to make significant contributions. Further, making these contributions provides a path to extend knowledge both in the subject and the application of computers to that subject.
The project mailing lists provide sometimes unvarnished views into the design and development process that is unavailable in any textbook. These JBoss lists include dev, design and development discussions, user, end user questions and discussions, and issue, for bugs and enhancements, lists for dozens of open source projects.