Many developers may not be aware of it but Gravity Forms has a full featured API available for implementing customizations and 3rd party integrations.
Gravity Forms developer Steve Henty has published a fantastic overview of the Gravity Forms API, including sample code, over at his personal blog. We highly recommend Gravity Forms users and developers check it out!
Steve has also published several other great Gravity Forms tutorials focusing on developer features. Check out his tutorial on Gravity Forms as part of a developer platform and his approval workflow add-on tutorial and be sure to follow his blog!