Aspen is a python web framework based in the filesystem, mixing controller and view in the same archive, it's called a Simplate.
We had some static html files in production, but months later we needed to add some server logic to this ones, without changing any url and having it integrated fast in our actual environment. These conditions make us think in this framework, it is perfect for this kind of situation, we hadn't to change our actual filesystem for our html files and we could have easily integrated this new logic inside them. :-)
Our main problem using aspen is the lack of documentation, in my opinion is really poor and it could explain more and better basic things, such as requests handling. Anyway, I like to explore the code but sometimes you don't want to spend some time in it when you have to get things done.
I have been using Django and Flask and I could say I found basics less intuitive in aspen than the others. I will try to explain what I meant in a later post when I get deeper in it.