We have been working with Cornish College of the Arts since they were still running ExpressionEngine 1.x. They are using two of our favorite technologies together - ExpressionEngine and FoxyCart. They recently upgraded to ExpressionEngine 2.9 and FoxyCart 2.0 which was a pretty major upgrade. With an upgrade of this size, a lot of the custom EE work that we had done for them back in the ExpressionEngine 1 days was no longer working, so they called on us to completely overhaul their course inventory management system.
Green Egg Media built a completely custom ExpressionEngine module that parses the FoxyCart XML data feed in order to make sure that they are not over-registering their summer extension courses. This module was built "the EE way" so that it is completely portable and can be used in the future, even if they end up changing the way they have their Channels and Channel Fields configured.