EAV-Django is a reusable Django application which provides an implementation of the Entity-Attribute-Value data model.
The application grew from an online shop project, so it is pretty practical and not just an academic exercise. The main priorities were:
a) flexibility of data,
b) efficiency of queries, and
c) maximum maintainability without editing the code.
Of course this implies trade-offs, and the goal was to find the least harmful combination for the general case.