  As blockchain-based systems see wider adoption, it becomes increasingly
critical to ensure their reliability, security, and efficiency. Running
simulations is an effective method of gaining insights on the existing systems
and analyzing potential improvements. However, many of the existing blockchain
simulators have various shortcomings that yield them insufficient for a wide
range of scenarios. In this demo paper, we present Zelig: our blockchain
simulator designed with the main goals of customizability and extensibility. To
the best of our knowledge, Zelig is the only blockchain simulator that enables
simulating custom network topologies without modifying the simulator code. We
explain our simulator design, validate via experimental analysis against the
real-world Bitcoin network, and highlight potential use cases.
