In a 2013 journal article titled "A Scalable Module System", Florian Rabe and Michael Kohlhase propose a module system called MMT (Modules for Mathematical Theories) for structuring mathematical knowledge.  The paper has a very interesting general discussion of module systems, from programming languages but also other areas like algebraic specification and theorem proving.  The system is based on a rather small set of concepts which subsume those of, for example, Standard ML's module system.  Thought-provoking!