Building an API? - Interacting with a CI Application OffSite

[eluser]Corey Freeman[/eluser]
This may be a stupidly ambivalent question, but can someone guide me in implementing an API?

Similar to twitter followers/tweets, I'd like people to be able to pull their account info from my site (cloudreve.com/home/) and display it on their websites.

I setup an RSS feed but I'm thinking that's not the best way to do it?