SMART on FHIR builds on top of FHIR for cross-EHR applications. In their words (http://smartplatforms.org/for-developers/):
"SMART on FHIR takes advantage of a new and powerful set of health data standards called Fast Healthcare Interoperability Resources, or FHIR. By using HL7’s FHIR for the clinical data layer, SMART offers a standards-based platform with broad reach, a rich set of detailed models, and the opportunity to create population-level as well as patient-level apps. SMART on FHIR also uses an updated set of authorization and authentication standards including OAuth2 and OpenID Connect."
and
http://jamesagnew.github.io/hapi-fhir/
(extension to the HL7 Java API "Hapi" which deals with FHIR and is (IMO) one of the more full-featured implementations of FHIR)
Disclaimer: I used to work for a major EHR company but no longer do so.