Mark Thoma is building an “open source” repository for economic models. Well, sort of open source. Unfortunately none of the four models included so far, nor the initial post, which Thoma says is open source, say anything about copyright or licenses.
Unfortunately under this default copyright regime, explicit licensing (or dedication to the public domain) is required for an open source project to scale. If five people contribute to a model posted to Thoma’s repository none of the contributors, including the original author, nor anyone else, has any right to distribute the resulting model, or allow others to further modify the model.
That’s why open source projects use explicit open source licenses and open source repositories require each project in the repository to use an explicit license. That’s what an open source economic models repository, or indeed any repository that wants to emulate the open source model, should also do.
NB creators of open source economic models may wish to consider an open source-like license intended for “content” rather than code, e.g., the Free Documentation License (that’s what Wikipedia uses) or a liberal Creative Commons license (e.g., Attribution or Attribution-ShareAlike).
Also see the open access movement, commons-based peer production and Science Commons. I don’t know how familiar the mainstream economics profession is familiar with these concepts, but “they” ought to be.