I need to create a very basic Gravity Forms add-on to send form submissions to an external API. I'm starting with email subscriptions, but will eventually also want to use this API for credit card processing. I haven't been able to find any documentation on creating my own add-ons -- does anyone have any resources they could share?
The basic email subscription functionality I'm looking to implement is demonstrated here: http://www.moiagroup.com/archives/using-the-ngp-api/664 -- all that is required is creating a new class object. Any idea what the simplest way to implement a Gravity Forms addon that would handle this would be?