There are two distinct modes available with the Ruleengine JaRE:
1) Application mode:
Run the ruleengine standalone respectively embeded in your Java application. Of course you can also use Java related languages such as e.g. Groovy.
If you use the Pentaho ETL Tool (PDI aka Kettle) you can use the ruleengine plugin to run the ruleengine inside your transformation.
In this mode all results and logging is available inside the application that utilizes the ruleengine. Of course it also uses the CPU and memory of the clients machine.
2) Server mode:
When you run the ruleengine in server mode, it runs on a defined host (also virtual or containerized of course) and a defined port. Use a socket connection to connect to the ruleengine.
If you use the Pentaho ETL Tool you can use the ruleengine client plugin to connect to the host that runs the ruleengine. In this case the ruleengine returns the minimum required result details to the client - compared to the application mode - and the details are conserved and logged on the server.
And of course the ruleengine is using the resources of the server for the business rules computations and not the resources of the client.
Both modes have their advantages and you can freely choose which one fits better your needs. The ruleengine is lightweight and the rulemaintenance web application allows to easily construct complex rule logic and groupings of rules. All free software waiting for you to give it a try.