Simple Rule Engine from Ant's blog. Able to process MVEL and Javascript rules in JVM, or run on Node.js.
Version 2.2.0: See http://blog.maxant.co.uk/pebble/2015/08/22/1440237900000.html => Support for Javascript rules in JVM via Nashorn.
Version 2.1.0: See http://blog.maxant.co.uk/pebble/2011/11/12/1321129560000.html and http://blog.maxant.co.uk/pebble/2014/10/03/1412371560000.html and also http://blog.maxant.co.uk/pebble/2014/11/15/1416087180000.html for Node.js.
Also see the test classes, e.g. https://github.com/maxant/rules/tree/master/rules/src/test/java/ch/maxant/rules/blackbox, https://github.com/maxant/rules/tree/master/rules-java8/src/test/java/ch/maxant/rules/blackbox and https://github.com/maxant/rules/tree/master/rules-scala/src/test/scala/ch/maxant/rules/blackbox, or https://github.com/maxant/rules/tree/master/rules-js/test/rules-test.js.
Release Notes and Licence (LGPL) can be found here: https://github.com/maxant/rules/tree/master/rules/src/main/resources.