M7. The xSDK collaboration has a strong preference for packages to use an OSI-approved, permissive open-source license (e.g., MIT or BSD 3-Clause). All new packages will be required to use such a license. Current packages using other licenses are encouraged to relicense, where possible. Required dependencies must use an OSI-approved license that is considered compatible with the preferred permissive licenses for distribution purposes (see https://en.wikipedia.org/wiki/License_compatibility). Non-critical optional dependencies can use any OSI-approved license.
RATIONALE: The choice of a permissive open-source license is friendlier to use by commercial entities. Note that strong copyleft licenses (e.g., GPL) are not considered compatible with permissive licenses. Weaker copyleft licenses (e.g., LGPL or GPL v2 with runtime exception) can be considered compatible for xSDK distribution purposes. Licenses that restrict commercial use are not acceptable in the xSDK. In the future, xSDK leadership reserves the right to define a build where packages with weaker copyleft licenses (e.g., LGPL or GPL v2 with runtime exception) are optional, so that users who wish to avoid these restrictions can do so.