GNU Octave - GNU Octave is a programming language for scientific computing.
Digital - A simulator for digital circuits.
MATLAB - A high-level language and interactive environment for numerical computation, visualization, and programming
LTspice - LTspice® is a high performance SPICE simulation software, schematic capture and waveform viewer with enhancements and models for easing the simulation of analog circuits.
BOOLR - Open-source digital logic simulator
MapleSim - MapleSim is an advanced system-level modeling tool that enables innovation and reduces development risk.