This talk will focus on how a Lagrangian perspective on dynamics is used to capture the time evolution of complex systems, e.g., granular flows, fluid-solid interaction problems, etc. In this context, the aspects that turn out to be more challenging are tied to the handling of friction, contact, geometry, large deformations and numerical solution scaling. The talk will highlight modeling and numerical solution techniques developed to address several of these challenges. Our solution methodology contributions have been implemented in an open-source simulation platform called Chrono, which is available on GitHub and used by hundreds of individuals to analyze large multi-physics dynamics problems. The talk will touch on several applications tied to granular dynamics, 3D printing and additive manufacturing, robotics, and ground vehicle mobility.