FreeCAD - https://www.freecadweb.org/
FreeCAD is an open-source parametric 3D modeler made primarily to design real-life objects of any size. Parametric modeling allows you to easily modify your design by going back into your model history and changing its parameters.
Open Cascade Technology - https://dev.opencascade.org/
is an open-source software development platform for 3D CAD, CAM, CAE, etc. that is developed and supported by Open Cascade SAS.
Kratos Multiphysics (A.K.A Kratos) is a framework for building parallel multi-disciplinary simulation software. Modularity, extensibility and HPC are the main objectives. Kratos has BSD license and is written in C++ with extensive Python interface.
Gmsh - https://gmsh.info/
A three-dimensional finite element mesh generator with built-in pre- and post-processing facilities.
blender - https://www.blender.org/
Blender is the free and open source 3D creation suite. It supports the entirety of the 3D pipeline—modeling, rigging, animation, simulation, rendering, compositing and motion tracking, video editing and 2D animation pipeline.
appleseed - https://appleseedhq.net/
appleseed is an open source, physically-based global illumination rendering engine primarily designed for animation and visual effects.
Sverchok - https://github.com/nortikin/sverchok/
Sverchok is a powerful parametric tool for architects, allowing geometry to be programmed visually with nodes.
KiCAD - https://kicad.org/
A Cross Platform and Open Source Electronics Design Automation Suite.
MBDyn - https://www.mbdyn.org/
MBDyn features the integrated multidisciplinary simulation of multibody, multiphysics systems, including nonlinear mechanics of rigid and flexible bodies (geometrically exact & composite-ready beam and shell finite elements, component mode synthesis elements, lumped elements) subjected to kinematic constraints, along with smart materials, electric networks, active control, hydraulic networks, and essential fixed-wing and rotorcraft aerodynamics.
openMDAO - https://openmdao.org/
An open-source framework for efficient multidisciplinary optimization.
GNU Octave - https://www.gnu.org/software/octave/
Scientific Programming Language, Drop-in compatible with many Matlab scripts.
Modelica - https://www.modelica.org/
The Modelica Language is a non-proprietary, object-oriented, equation based language to conveniently model complex physical systems containing, e.g., mechanical, electrical, electronic, hydraulic, thermal, control, electric power or process-oriented subcomponents.
OpenModelica - https://www.openmodelica.org/
OPENMODELICA is an open-source Modelica-based modeling and simulation environment intended for industrial and academic usage.
Mattermost - https://mattermost.com/
Mattermost is an open source platform for secure communication, collaboration, and orchestration of work across tools and teams.