TurboGears is a Python-based framework that enables you to quickly build database-driven, ready-to-extend web applications. TurboGears can be developed on Windows, Linux, and Mac OS X.
Django for Python is the most recently announced of what is becoming a long line of web frameworks inspired by Ruby on Rails. Others that have popped up include MonoRail for .NET & Mono, Subway for Python, Trails for Java, Catalyst and Maypole for Perl. In the context of all these rails derivatives, this article on "Could Rails have been built without Ruby?" is an interesting read