One of the use cases of the WSO2 Governance Registry is storing metadata information of different artifacts. In an Organization, there can be different metadata of different artifacts such their REST APIs, SOAP Services etc. In such a scenario you can use API and Service RXT which are available in the WSO2 Governance Registry to store metadata information.
With the use of API metadata which is stored in the WSO2 Governance Registry, you can publish APIs into WSO2 API Manager without accessing the web interface of the API Manager. This API creation is handled through lifecycle executor of the WSO2 Governance Registry. Once lifecycle state of the api publisher is reached, the executor will invoke Publisher REST API of the WSO2 API Manager and create the API. "Integrating with WSO2 API Manager" documentation explains about how to create an API using SOAP service meta data information.
If you want to create an API using the REST API metadata information available in the WSO2 Governance Registry, you have to write your own executor to achieve this. So I have written an example Implementation of the lifecycle executor which can used to create API's in the API Manager.