We are using an ERP system that advertises itself as open source. What it is, is a java based server (and client) which runs their own simple language (some sort of sql like language with conditionals etc) to build your business rules, processes. That bit is open (and sits in the database). You either write it yourself or pay them to do it. They even use a dongle so they can disable your instance in case of nonpayment of the yearly service fee.