How would you call the main software used by a company

I'm looking for a word designating the main software of a company. I know the term line of business application, but I never heard anyone say "this is our line of business application", only "this is a line of business application."

I'm looking for the term designating the class of software applications that are the only ones to be at the heart of a company. A CRM is in this idea, since we often say "this our CRM software"; however, the software I'm trying to qualify goes beyond customer relationship management as it also takes care of the daily operations.

Any ideas?

Enterprise Resource Planning software (ERP for short) is a set of integrated modules that allow you to control many, most, or all aspects of your business from a single package: financials (General Ledger, Accounts Payable, Accounts Receivable), order processing, purchasing, manufacturing, inventory management, time & attendance, payroll, etc.

Most companies run only one such system¹, unless they are dealing with an acquisition or merger; although it is certainly common to run an ERP system, but have elements that could be managed by that system run instead on some other software (for instance, many companies will have a separate payroll system, even if their ERP software has a payroll module available).

1: (Or they are trying to consolidate down to one system, or at least they wish they were running only one.)