Is there a Office 365 development API like Google Docs? I was searching web but I was unable to find.
There's an API for the Exchange part of Office 365. Lync also has an API. You can also managed Sharepoint sites via the Client Object Model, web services or WebDAV APIs for uploading and downloading files
However I don't believe there's anything for manipulating documents online outside of using WebDav to push to a sharepoint site.