1. A system comprising: one or more computer processors; a memory containing one or more applications; and a management controller communicatively connected to: (i) an out-of-band network for accessing the management controller and (ii) a private network of a first communications protocol and for communicating with an execution engine running on the system, the private network provided via one or more network interface controllers over a predefined link of a second communications protocol between the management controller and the one or more computer processors; wherein the management controller is configured to perform an operation for managing the system, the operation comprising: providing a first application programming interface (API) specifying one or more functions for managing at least a first one of the one or more applications, without requiring any driver associated with the first API to be provided for any operating system executing on the system; via the out-of-band network, receiving a first request for the first application to perform a predefined action that includes invoking one or more functions of a second API provided by an operating system executing on the system, wherein the first request invokes a function specified in the first API; and via the private network, sending the first request by operation of at least one computer processor to the execution engine to instruct the first application to perform the predefined action responsive to the first request; wherein the management controller is further configured to extend the first API during runtime to include a desired function not already included in the first API, by: receiving, via the out-of-band network: (i) a second request to extend the first API during runtime to include the desired function and (ii) business logic to associate with the desired function; and registering the desired function and the business logic with the execution engine by sending one or more messages to the execution engine via the private network, wherein the execution engine is configured to associate the desired function with the business logic.