FNCS 2.0 is a brand new implementation of the concepts established by FNCS 1.0 (https://github.com/GridOPTICS/FNCS). Cooperative simulation, or co-simulation, is the process in which at least two simulators solve initial-value differential equations that are coupled to each other. Data is exchanged at fixed time steps and no iteration is allowed between simulators to converge to a solution at any particular time step. In literature, this type of co-simulation is referred to as quasi-dynamic coupling, loose coupling, or Ping-Pong coupling (Hensen 1999, Zhai and Chen 2005). FNCS 1.0 extended these concepts by allowing variable time steps and speculative synchronization. FNCS 2.0 extends these concepts further by allowing simulators to reiterate during synchronization points. FNCS 2.0 also distills the concepts of FNCS 1.0 down to a simple, yet powerful, application programmer interface library.