While not really a framework, i've getting used to using webapp and appengine's ndb datastore (yes its an appengine application). The application doesn't serve html, only json (its basically an api).

The our app is build as an ios, android and webapp on top of this api.

It depends on what you're building. And sometimes this approach is not nice. But it works for our usecase.

In conclusion: sometimes your architecture doesn't need a full-fledged webapp framework.