2] FreeCAD FreeCAD is a CAD modeling suite that you can use to view IGS and other 2D/ 3D files in Windows 11/10. The other formats supported by it include STP, STL, PLY, OBJ, 3DS, DAE, DWG, DXF ...

The file types you can convert to are much more limited—there are only six of them—but Spin 3D includes outputs in 3DP and 3DX in addition to STL and OBJ formats.