It's always interesting to see the tools developers build to help them do exactly the things they need to do. CodePen, despite the fact that we don't really have an true "API", has spawned a number of such tools. Here's some of the ones on GitHub.
jhey tompkins created "a local development boilerplate set up for creating new Pens":
Because I'm not always online, but I want a quick and easy way to work on pens locally and then simply push them up to CodePen later. Plus, it's nice to have them all in version control.
This can be done either via a command line tool or from a provided download method.
Chris Bogardo gave himself a nice little shortcode for Embeds
An extension for cebe/markdown to provide a shortcode to embed codepens from http://codepen.io/ in your Markdown.
Alex Zaworski's Chrome Extension is on GitHub as well.
A Chrome extension meant to enhance the CodePen experience.
Konrad Dzwinel's DevTools add-on which can send DevTools-selected elements over to CodePen (styles and all!):
Chrome/Chromium extension that allows easy CSS+HTML extraction of specific DOM element. Created snippet can be then exported to CodePen, jsFiddle or JS Bin with one click.