Example of SFDCRules - https://github.com/JitendraZaa/SFDCRules

SFDCRulesExample.cls

//Define set of all allowed operators
//Mostly we don't need to change this, it can be added in setup method
Operations opObj = Operations.getInstance(); 
opObj.registerOperation(OperationFactory.getInstance('&&'));
opObj.registerOperation(OperationFactory.getInstance('==')); 
opObj.registerOperation(OperationFactory.getInstance('!=')); 
opObj.registerOperation(OperationFactory.getInstance('||'));
opObj.registerOperation(OperationFactory.getInstance('('));
opObj.registerOperation(OperationFactory.getInstance(')'));
opObj.registerOperation(OperationFactory.getInstance('<'));
opObj.registerOperation(OperationFactory.getInstance('<=')); 
opObj.registerOperation(OperationFactory.getInstance('>'));
opObj.registerOperation(OperationFactory.getInstance('>='));

//Define bindings, which will replace variables while
//evaluating rules		
Map<String, String>bindings = new Map<String, String>();
bindings.put('Case.OwnerName__c'.toLowerCase(), 'Jitendra');   
bindings.put('Case.IsEscalated'.toLowerCase(), 'false');  
bindings.put('Case.age_mins__c'.toLowerCase(), '62'); 

//Define rule
String expr  = 'Case.OwnerName__c == Minal || ( Case.age_mins__c < 75 && Case.IsEscalated == false )' ; 

//Initialize Rule Engine
Rule r = new Rule().setExpression(expr);   

//Evaluate rule with Binding values
Boolean retVal = r.eval(bindings) ;

//Check if expected result is correct
System.assertEquals(true, retVal);