If you're looking to get started with the Twitter, Facebook, Foursquare, or Tumblr
OAuth APIs then these pages are for you.

Twitter

The examples for the Twitter API that I have created are the most complete set that I've written. I've provided examples of doing the most commonly requested tasks. Get Started.

Facebook

Perhaps the easiest API to get started with due to it being based upon OAuth 2. Get Started.

Foursquare

Although the Foursquare OAuth API has only recently been created, the actual API behind it has been around for a while. These few examples will help in beginning your programming adventure with it. Get Started.

Tumblr

I'm still working on the documentation for the Tumblr OAuth API, it'll be here soon.