ngspice vs OpenSim

ngspice is a free, open-source simulator for electric and electronic circuits described as netlists. It handles analog, digital, and mixed-signal designs, with models for active, passive, analog, and digital elements; model parameters can come from collections, manufacturers, or foundries. Its SPICE compatibility supports PSPICE or LTSPICE device model parameters and netlists for discrete circuits. For mixed-signal co-simulation, it supports Verilog blocks compiled with Verilator and, since ngspice-44, VHDL blocks using GHDL. The OSDI/OpenVAF interface connects Verilog-A compact device models without requiring programming on the ngspice side. It can also be built as a shared library or DLL for another application to control. Listed integrations include KiCad, Autodesk Fusion, and Python interfaces such as PySpice. ngspice does not include schematic entry: input is through the command line or files. The stable download page offers source archives and Windows binaries; Linux users are directed to their distributor or source compilation, and the project's own macOS release is unavailable there.

OpenSim models and simulates how humans, animals, robots, and their environment move and interact. Its graphical interface displays models and supports creating and analyzing simulations. Models can contain rigid bodies, joints, constraints, contact, muscles, and other actuators. Movement analysis tools include inverse kinematics, inverse dynamics, static optimization, and forward dynamics; Computed Muscle Control can generate muscle-driven forward simulations. The API is usable through Matlab, Python, Java, and C++, and GUI scripting uses an embedded Jython shell. Plugins can add analyses and model components, but must be built for the same OpenSim version and platform. The graphical interface is distributed for 64-bit Windows and Mac, while there is no public Linux GUI distribution; the API source can be built for Linux. OpenSim is free and open source under Apache 2.0, though models, examples, and plugins may have separate licenses. It is intended for research and teaching and welcomes academic and commercial applications. Documentation, tutorials, and a discussion forum are available. Downloading requires a SimTK account.