Tornado is great as a standalone API/WWW server, but for WSGI-based environments, like Google App Engine, I would choose Flask (>= 0.7.1) over any other framewo

Tornado is great as a standalone API/WWW server, but for WSGI-based environments, like Google App Engine, I would choose Flask (>= 0.7.1) over any other framework. Flask, despite being a micro-framework, is extremely powerful. It's core is well-written and there's a lot of useful extensions out there (like Flask-WTF or Flask-Assets). Flask also works really well with Google App Engine (see example skeleton: https://github.com/kamalgill/flask-appengine-template https://github.com/kamalgill/flask-appengine-template; there's more on GitHub). With little effort you get WTForms and even Webassets support almost out of the box, in really elegant way. Tornado will also do, since it's very similar to webapp and has very good templating system. However, since extensions ecosystem for Tornado is almost non-existent, one has to write more code to make up for it (e.g. integration with Webassets, management commands, OAuth support etc.). There's also Tipfy, but I have absolutely no experience with it, so I can't vouch for it.