As of this commit I have added a CITATION.cff file (as @jjahan recommended) and a LICENSE file to the Calculation Engine repo, selecting Mozilla Public License Version 2.0. MPL-2.0 is the most permissive of the “copyleft” licenses: it only requires that any of our source code used in derivative works must be included in the distribution along with the license. This means, for example, that if a group decided to run their own version of the Calculation Engine derived from ours, they would only have to publish the source files of ours they used, but all their own additional code could remain closed source. For us this is honestly primarily useful as a way to effectively enforce citations of the CE in the context of software products, where there is otherwise not the same tradition of citation as in academic journal publications.
@nyunes For the sake of clarity: We are clearly much less concerned with re-use of the software itself in derived software products than we are with academic citation when people publish results generated by the CE. These are two separate issues. The CITATION.cff file will help with citations, and we will provide citation instructions (e.g. bibtex snippet) on the CE home page.