TUFTSim is the newest version of the circuit simulator, written in C++. TUFTSim is the successor to the MCS simulator, which was written in C. TUFTSim was written using MCS as a starting point, expanding and improving upon its predecessor. TUFTSim allows for concurrent fault and multiple domain concurrent simulation algorithms, accepting and simulating multilevel models efficiently and accurately. Multilevel concurrent simulation was present in MCS, but TUFTSim introduced gate level and behavioral simulation in multiple domains. TUFTSim is also a discrete-event fault simulator, just like MCS.