License for Project Jupyter software

[jasongrout]

In the Jupyter governance, it indicates that when a project is adopted by Jupyter, it should use the license specified in the governance: https://raw.githubusercontent.com/jupyter/governance/master/projectlicense.md, which is BSD.

According to this, the license in, for example, https://github.com/jupyter-widgets/ipyleaflet/blob/master/LICENSE probably should have been changed from MIT to BSD when it was adopted as a Jupyter project.

However, according to the main governance document, "The Software developed by The Project is released under the BSD (or similar) open source license". I think MIT would qualify as "similar" to BSD.

So which is it? If a project is incorporated into Jupyter, should it be converted to BSD for consistency with other Project Jupyter software, or is it fine to stay, say, MIT licensed? ("converting" I think more properly means that the LICENSE file changes to BSD, but it retains the MIT copyright notice for code before it was adopted into the project)

It would good for us to have clarification on the intent and our interpretation. I don't know of any other Project Jupyter projects that are released under licenses other than the standardized BSD project license.

CC @ellisonbg (original author of ipyleaflet), @SylvainCorlay and @martinRenou (main current maintainers) of ipyleaflet.

For the record, I'm okay with an official subproject being MIT licensed if it was licensed MIT before being adopted. I think new projects that start in Project Jupyter should carry the project license.

[choldgraf]

My thinking is that we should accept 1 or a couple explicit licenses that we'll allow, rather than using more vague language like 'or a similar license', in order to avoid the extra labor and ambiguity associated with deciding whether a license is "similar" or not.