If no-one is making money off of the project, not off ads, not off merchandising, and you are not doing it as implicit advertising for paid services, then it is probably permitted.
Consider for example that File Exchange contributions effectively become Open Source.
If it were being done under the name of a large organization (e.g. Free Software Foundation) then the organizations that get large enough tend to get monetary donations and probably you could not use the Home license in such a case. If the organization the work is contributing to has employees, it might be past Mathworks' boundaries.
