Open core is a business model for the monetization of commercially produced open source software. Coined by Andrew Lampitt in 2008, the open core model primarily involves offering a "core" or feature-limited version of a software product as free and open-source software, while offering "commercial" versions or add-ons as proprietary software.
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Controversy
The concept of open core software has proven to be controversial, as many developers do not consider the business model to be true open source software.
Despite this, open core models are used by a large number of open source software companies.
Use of contributor license agreements
Some open core products require their contributors to sign a contributor license agreement, which either dictate that the copyright of all contributions to the product become the property of its owner, or that the product's owner is given an unlimited, non-exclusive license to use the contributions, but the authors retain copyright ownership. In an open core scenario, these agreements are typically meant to allow the commercial owner of the product (which in some cases, is ultimately the copyright holder to all of its code, regardless of its original author) to simultaneously market versions of the product under open source and non-free licenses. This contrasts more traditional uses of CLAs, which are meant solely to allow the steward of an open source project to defend its copyright, or guarantee that the code will only ever be made available under open source terms, thus protecting it from becoming open core.