Magento being an ecommerce platform running at a pace of a dragster, its highly difficult for its competitors to keep up with its features, updates, community base and no. of organizations using it.
Now the organizations using it also uses/need other subsystems for the tasks which Magento is not programmed/supposed to do. For example, to maintain accounting records organizations using Accounting Systems such as Quickbooks, using POS Systems such as Microsoft RMS, iVend, Lightspeed Retail for physical stores, using ERP such as SAP Business One, MS Dynamics NAV, Open ERP for order processing, accounting and for a full business management cycle, using Shipping Systems and Tax Management Systems such as Avalara or Exactor etc. For a smooth data flow and proper information management organizations are also using some Plugins/Connectors which connects these back office systems with the Magento eCommerce.