Which API use HTTP meddages to tansfer data to applications residing on different host ?

OpFlex is a Cisco-developed policy protocol for Software-Defined Networking, not a general API style using HTTP for data transfer.

REST (Representational State Transfer) is an architectural style for APIs that primarily uses standard HTTP methods (GET, POST, PUT, DELETE) for stateless communication and data transfer, typically in JSON or XML format, between applications residing on different hosts.

OpenStack is a collection of open-source tools for cloud computing, and while its services expose RESTful APIs, OpenStack itself is not the API style that uses HTTP messages.

OpenFlow is a protocol used in Software-Defined Networking to communicate between the control and data planes, instructing network devices, and it does not use HTTP messages for general application data transfer.