Context: In recent decades, many financial markets and their participants have changed their working method from a completely manual and traditional one to an automatic one, benefiting from complex software systems. There are different approaches to the development of such software systems. Objective: In this paper, we study the application of the Multi Product Line (MPL) approach in the software ecosystem (SECO) of the equity market. By profiting from the concepts and practices of the MPL approach, we want to design a SECO that makes the real-time and automated flow of financial transaction data between market participants' software pieces possible. Method: We first provide some background information about the equity market, its participants and their relations, and two primary order life-cycles in which these players cooperate. After that, we analyze the variability in each market participant's software. Next, we describe the employed architecture and the implementation approach. Finally, we discuss three scenarios by which the whole proposed SECO is tested and validated. Results: To implement the mentioned working method, named Straight-through Processing (STP), different technical and non-technical elements' contribution is essential. Attaining success in developing the equity market's SECO addresses the technical aspect and prepares the technical infrastructure for the rest of the work. Conclusion: The successful validation of the equity market's SECO indicates that the adoption of the MPL approach is a viable strategy for the development of equity market SECOs. It also suggests that this approach is worthy of more attention and investment.