I have a question about the use and attribution of internal software tools.
We have a model in our group that is very popular and has formed the basis of many student projects and publications. It was written about five years ago and has been published as a book chapter, but not a journal paper. The model exists primarily as source code; there is no compiled version per se although there is a user interface tool that generates new source based on the template of the original model. As a result, new work tends to involve a mix of the original code and further modifications as appropriate for the study in question.
At the moment, we don't want to release the underlying model as open-source. Is there an appropriate license that people would recommend to clarify these usage principles? The original model author now has a looser affiliation with our university and so it may become difficult to ask his opinion on a case-by-case basis.