Hi prateek,
Are you looking for OpenEMR API mentioned in the following link?
http://www.open-emr.org/wiki/index.php?title=OpenEMR_API
This API feature is still in early phase to auto-document the OpenEMR codebase.
OpenEMR is also looking to come up with FHIR(RESTful API) enabled OpenEMR.
Know more about FHIR,follow the below links :
http://hl7.org/fhir/modules.html
Thanks,
ViSolve