A software license is a legal instrument governing the use or redistribution of software.
Since the 1970s, software copyright has been recognized in the United States. Despite the copyright being recognized, most companies prefer to sell licenses rather than copies of the software because it enables them to enforce stricter terms on redistribution. Very few purchasers read any part of the license, initially shrink-wrap contracts and now most commonly encountered as clickwrap or browsewrap. The enforceability of this kind of license is a matter of controversy and is limited in some jurisdictions. Service-level agreements are another type of software license where the vendor agrees to provide a level of service to the purchaser, often backed by financial penalties.
Copyleft is a type of free license that mandates derivative works to be licensed. The other types of free license lack this requirement: for permissive licenses, attribution is typically the only requirement, and public-domain-equivalent licenses have no restrictions. The proliferation of open-source licenses has compounded license compatibility issues, but all share some features: allowing redistribution and derivative works under the same license, unrestricted access to the source code, and nondiscrimination between different uses—in particular, allowing commercial use.
Free and open | Non-free | |||||
---|---|---|---|---|---|---|
Public domain[1] and equivalent licenses | Permissive license[2][3] | Copyleft[2][3] | Noncommercial license[4] | Proprietary license[5] | Trade secret[6] | |
Description | Waives copyright protection | Grants use rights, including right to relicense (allows proprietization, license compatibility) | Grants use rights, forbids proprietization | Grants rights for noncommercial use only. | Traditional use of copyright; no rights need be granted | No information made public |
Notable software licenses | PD, CC0[7] | MIT, Apache, MPL, BSD | GPL, AGPL | JRL[8] | Proprietary software |