The reasons for introducing the concept of the entrostat in statistical physics are examined. The introduction of the entrostat has allowed researchers to show the possibility of self-organization in open systems within the understanding of entropy as a measure of disorder. The application of the laws written down for the entrostat has also allowed us to formulate the “synergetic open system” concept. A nonlinear model of the activity of a medium-sized company in the market is presented. In the course of the development of this model, the concept of the entrostat was used. This model includes the equation of a firm’s market activity and condition of its stability. It is shown that this stability depends on the income of the average buyers of the firm’s goods and furthermore that the equation estimating the firm’s market activity includes the scenario of a subharmonic cascade, which ends in chaos for the majority of market participants, i.e., in an economic crisis. The feature of this paper is that the decision containing the scenario of the subharmonic cascade is found analytically (instead of numerically, as is customary in the current scientific literature).