Adaxa site best explains with this write up.
http://www.adaxa.com/erp/ It is an ERP subject matter that professionals can make sense of when Compiere first came about in 1999 and iDempiere as a fork of it, retains this important functional model (similar to what Openbravo and ADempiere as been similar forks.)
However the edge that iDempiere here has is (1) OSGi adoption, (2) Active community of contributors (3) Best ERP mentioned in BOSSIE Infoworld 2015 Award.