The open-source model is a more decentralized model of production, in contrast with more centralized models of development such as those typically used in commercial software companies. Scientists view the open-source model as a case of open collaboration. A main principle of open-source software development is peer production, with products such as source code, "blueprints", and documentation available to the public at no cost. The open-source movement in software began as a response to the limitations of proprietary code. Since, its principles spread across different fields to become what is known as open collaboration. This model is also used for the development of open-source appropriate technologies, and open-source drug discovery.