Open Source is a term, developed in 1997, that represents free software. The term was designed to emphasize the freedom of use aspect of the software (source code is open), and not allow people to assume free meant no cost (which it did not). Aside from the marketing aspect of the new term, there are also differences in the ideologies of the proponents of the open source movement as a 'branch' of the free software movement. The open source movement (Eric Raymond et al.) believes that open source should be a business choice, and only appropriate when it makes business sense (Magic Cauldron paper discusses this). The free software movement (evangelized by Richard Stallman) believes that all software should be free, and only if all software is free will free software be truly effective. Since all software development relies on previous 'knowledge', and that previous knowledge is public domain, then new knowledge, as a derivitive, should also be free. While Open Source software must have a no-cost alternative (for it to comply with the open source definition) a marketer can sell a version at a price. (Red Hat's version of the Linux operating system is a great example.) The software releases are done so with the source code, which allows the consumer/user to modify the code for its specific purpose. Users that do modify the code are asked (via the license) to submit any modifications back to the initiators of the project (submitting a patch). This allows any improvements, or resolved bugs, to be included in new releases of the product. The most important developments thus far in the open source and free software movement has been the evolution of the Linux operating system, started in 1991, and the announcement of Netscape's Mozilla project, in 1997. Firefox is a forked iteration of the Mozilla project.