One Ring isn’t like other "Rules Engines", it’s meant to be used as a web service (SOA) for multiple applications to gain access to scripted processing of arbitrary parameters.
It centralises processing of common rules (or business rules) for multiple applications that need access to the same rules. Rules are defined using a simple language understood by domain experts.
One Ring is aimed at continuous processing for multiple small applications, not batch processing of billions of entities. It is very light weight and is deployed as a WAR inside a container like Tomcat. You can have multiple One Ring servers running in the same container pointing to different, or the same rule sets.
It has not been optimised for speed, but it’s not exactly slow. The engine can process a 1000 simple 3 rule rule sets in around 200ms or ~0.2ms per rule set. That’s serially called with fact set-up in each call.