Giblets is a simple plugin system based on the component architecture of Trac. In a nutshell, giblets allows you to declare interfaces and discover components that implement them without coupling.
The Giblets project also includes plugin discovery based on file paths or entry points along with flexible means to manage which components are enabled or disabled in your application.
The full documenation for giblets is available at http://ltucker.github.com/giblets.
pip install giblets
You can also install the current development version of giblets with pip install giblets==dev or easy_install giblets==dev