Maybe check out SmartRules. Its not free, but the interface looks simple enough.
Only know about it because I've used the SmartCode codegen utility from there before.
Here is an example rule from the Website:
BUSINESS RULES IN NATURAL LANGUAGE
Before
If (Customer.Age > 50 && Customer.Status == Status.Active) {
policy.SetDiscount(true, 10%);
}
After (with Smart Rules)
If Customer is older than 50 and
the Customer Status is Active Then
Apply 10 % of Discount