FCSTD files are used in FreeCAD, an open-source parametric 3D CAD modeler. Opening an FCSTD file is simple with FreeCAD, which allows you to design 3D models, create 2D drawings, and render designs. To open an FCSTD file, you can simply launch FreeCAD and use the 'File' > 'Open' option to browse and select the FCSTD file you want to open. Once the file is open, you can use FreeCAD's tools and features to modify, analyze, and export the 3D model. FreeCAD supports a wide range of file formats, making it a versatile tool for 3D modeling and design. If you're new to FreeCAD, there are plenty of tutorials and resources available to help you get started with creating and working with FCSTD files. With FreeCAD, you can unleash your creativity and design skills to bring your 3D projects to life.