In a large chip, an asynchronous Network-on-Chip (NoC) is a suitable candidate for establishing an interconnection network between varied components. Architectural level simulation is an accepted methodology for evaluating such systems. In this paper, we propose a fast and versatile Asynchronous Network-on-Chip (NoC) Simulator - ANSim, which brings down the simulation time by 25 x, compared to the state of the art simulators. It can model and analyze all synchronous, asynchronous and mixed synchronous-asynchronous system of cores connected through NoC. ANSim can model routers with different delays, routers with asynchronous arbitration, connected in a wide range of topologies. ANSim supports individual routers modeled to have varying timing constraints. Further, it supports synthetic and real-workloads and produces system-level latency, throughput, power, power-gating and arbitration reports. ANSim has been verified against RTL models of NoCs and other RTL verified simulators. An open-source synchronous NoC router, TNoC and its asynchronous derivative are used to demonstrate ANSim's usefulness and features.