The open-source model is a decentralized development model that encourages open collaboration. A main principle of open-source development is peer production, with products such as source code, blueprints, and documentation freely available to the public. The open-source movement in software began as a response to the limitations of proprietary code. Open source promotes universal access via an open-source or free license to a product’s design or blueprint, and universal redistribution of that design or blueprint. Before the phrase open source became widely adopted, developers and producers used a variety of other terms.