This page lists all of Facebook's APis [url].
Everyone is invited to suggest and list APis on this page and anyone and anywhere can help describe APIs. Writing on this website is very simple. Please visit the Help page for easy-to-follow instructions.
The resources are here [url].
G's APIs Explorer lists them all [url].
Their developers' page [url]
Twilio API docs [url]
Visit Twitter Developer page [url]
Yahoo! Developer Network has good descriptions of their APIs and tools [url].