They're just modules by another name. The way I think about design is usually centered around the data model, so if some subject has a number of ORM models and

They're just modules by another name. The way I think about design is usually centered around the data model, so if some subject has a number of ORM models and is pretty self contained it makes sense to put them in their own app, together with related urls and views and stuff. They still live in the same repository and aren't meant to be re-used, just split into logical parts to make the code base easier to think about. Modules, in other words.