I understand the term used all over social networking sites is "API",
I did some research on the web, and it seems to be a very big topic to cover.

As per my previous post, I have made a social networking site using asp.net 3.0 and C#. It's a small prototype.

A few tables such that the record of friends and their friends and their interest is kept. There are no privacy constraint at the moment

What I would like is to, "welcome developers please download the API for free and start making applications for the social network". Consider application extracts interests of the friends of a friends who is using the application.

From what I understand, an API is a space to host an application either provided by me or the developer.