The objective of reaching net zero emissions of greenhouse gases set out by the European Climate Law (Europe-an Parliament, 2021) requires significant changes in the mobility sector. Today, most emissions in this sector are caused by cars equipped with combustion engines (Umweltbundesamt, 2023). Thus, providing competitive sus-tainable alternatives to motorized individual transport is generally considered to be a critical factor for a successful transformation. When bundled as easy-to-use Mobility-as-a-Service (MaaS) offerings, integrated multimodal mobili-ty systems can provide such an alternative (Ministerium für Verkehr des Landes Nordrhein-Westfahlen, 2022). However, due to their heterogenous nature, high variability and large size, the analysis and planning of their struc-ture raises several challenges. The goal of the MobyDex research project (MobyDex Consortium, 2024) is to address these challenges by provid-ing a software platform that enables detailed analyses of multimodal mobility systems at a regional level. The core abstraction introduced by MobyDex is a multimodal mobility index that precisely captures the actual mobility offers and demand. To gather the system state, MobyDex integrates real-time status data from public transportation and micro-mobility providers as well as floating-car-data and movement data generated by cellular networks. By con-trasting different components of the mobility index, MobyDex can support a broad range of applications. In this paper, we describe the high-level architecture of the MobyDex platform. Thereby, we present the structure of the underlying mobility index, and we discuss how it can be used to support a broad spectrum of applications. Finally, we derive resulting technical and scientific challenges and outline how they will be addressed by MobyDex.