Some Gnumeric stuff

The official Gnumeric vodka bottle

vodka bottle

Python

Programming Gnumeric using Python
You can write extra functions and file savers/loaders in Python. Charles Twardy wrote a nice tutorial, which is now included in the official Gnumeric documentation.
A plugin example
This example adds in a few extra spreadsheet functions. They are not useful - the useful functions are in Gnumeric already :-) - they are just to show how to do it. You can also see how to call a spreadsheet function from Gnumeric.
GUI plugin example
This plugin demos the UI support which was added in 1.2.x, but is still considered experimental.