I don't see the revolutionary in Nagare. It doesn't have active community (check the list of nagare based projects: http://pypi.python.org/pypi?%3Aaction=search&term=nagare and Nagares blog: http://www.nagare.org/trac/blog). The composition concept is also included in Pyramid / Flask / Tornado. There are also a lot of html builder (so there is no point to develop other one which is bind to Nagare).
Besides this it is interesting.
Flask has manual routing. Nagare creates URLs and binds then to Python actions automatically. It also has a global session object as opposed to indepedent sessions per Python object.
All three of those are trapped into the paradigm of receiving URLs and routing them to python methods.