Point given for "write my own ERP software."
I work with that stuff on a daily basis, and
am actually thinking of trying just that.
That's because no 2 ERP deployments are the same: you either have a rigid, fully bespoke system that's "easy" to develop, but can't be used anywhere else. OR you have a gigantic ERP system that has knobs up the wazoo for customizability, which supports an entire industry of consultants that do installation & configuration (like SAP)