I had another look at moodle (open source vle) and remembered that I had found a lot to like in it. It offers flexibility in course structure and enables sequencing and co-location of many types of content (incl assessments and discussions). It was designed to enable a constructionist approach and incorporates learning journals. One of the demo courses has teacher-level access.
Anyway - I don't know how scalable and maintainable it is, but useful as a reference point for ways of structuring course materials.
I was reminded of it by this very comprehensive list of LMS and VLE systems (might come in handy) - scroll down for links
