These are Blender or other models exported to X-Plane / WED obj-8 format. The textures applicable are in the Textures folder and must be installed in the same directory with the obj files. A growing number of draped polygons (.pol) are included here created as needed.
I began using AC3D to build models for export, with the plugin (ac3d_plugin_win_321r2) but have switched for most of my modeling to Blender and Xplane2Blender plugin. Occasionally I do pre-design constructions with FreeCADhttps://www.freecadweb.org/.
I believe in and support open source software whenever I can.
These objects my be inspected individually using the objView utility which is part of the XPTools package.