MiniFB is a small, lightweight Ruby library for interacting with the Facebook API. A demo application that uses Rails with MiniFB is provided to show the library in action. MiniFB is offered by Appoxy, a web application development company.
Expion, a Social Media Management System (SMMS) company, specializes in helping companies manage their brand images on social networks, from Facebook to Youtube to Twitter, often relying on partners' APIs to pull of some of their more interesting feats. Most recently, it was chosen by Google as a Google Plus API partner for the brand-focused Pages feature.
Google Buzz is a new service that takes aim at Facebook and Twitter by providing the ability to post links, photos and status updates directly from your Gmail account. And right off the bat Google has released the accompanying API.