So who was first Idiom or Microsoft? They both use the concept of defining the datamodel by XSD schema's and use drag-and-drop to place these elements in rule constructs. The advantage of Idiom here is that you seem to be able to show multiple rules at once. This is really missing in the Business Rule Capturing environment of MS Biztalk 2004. They also seem to be able to integrate with BPEL so that must be pretty close to Biztalk rules format. Have a look at their Decisions and Formulas demo.
What still surpise me is that also Idiom expects the Rule writer to define XSD schema's. Why can't we leave the technical binding to XSD, Databse, Java beans or C# components out of the Rule Definitions? Writing good business rules is already complicated enough!