Etlworks Integrator can be used as an Enterprise Service Bus, serving requests from third-party applications. Basically, you can build an API that other applications can use to send a payload to Etlworks Integrator or request enriched data from Etlworks Integrator without writing a single line of code.
The event-driven Flows are the extract data from source, transform, and load in destination Flows where either source or destination is a Listener.
The other name for event-driven Flows is user-defined APIs. Read how to create user-defined APIs in Etlworks Integrator.