Pylons
Pylons is an excellent web app framework. It is very flexible, powerful, pythonic, and modular. It is based on wsgi specification and the model-view pattern. So far it is the easiest one I've worked with. Its design makes sense and suits my needs wonderfully.
At its core it is really a collection of independent middleware components. The framework is built up when the app launches. This design means you can easily customize almost every aspect of your deployment.
You can change the template language, the database connector, the form handler, and authentication system. You can easily add your own features. And its design makes it easy to integrate third party components, whether they have been designed for Pylons or not.
Out of the box it uses Mako for templates, SQLAlchemy for databases, and Paste for a bunch of things.
One of the best things is the built in online debugger. If you app throws an exception it is caught and the page turns into an interactive debugger with tracebacks and a functional python command shell. It's great! It makes development a breeze.
The main site for Pylons is PylonsHQ.com. There's great documentation at PylonsHQ Docs 0.9.7. To install it see the Getting Started page.
The projects source control uses Mercurial. You can clone the main development trunk with:
hg clone https://www.knowledgetap.com/hg/pylons-dev Pylons