Ruleby is a rule engine written in the Ruby language. It is a system for executing a set of IF-THEN statements known as production rules. These rules are matched to objects using the forward chaining Rete algorithm. Ruleby provides an internal Domain Specific Language (DSL) for building the productions that make up a Ruleby program.
If you prefer a journalistic approach, we have a short blog post that gives an Introduction to Ruleby. Or you can just find the answers to some of your questions and learn who is using Ruleby in our FAQ.