ObjView is a 3-d viewer for X-Plane object files (version 2 and version 7).  X-Plane has three major revisions of the ".obj" format, none of which are related to other public .obj formats, all of which are text:
Within each major type of object file, soem features were added to the format later; users of the latest version X-Plane 6 (6.70) or 7 should not have any problems with this.  ObjView does not support original Obj version 1 files.

Using ObjView

To use ObjView, simply double click the application and drag an .obj file into the window to view it.  The mouse wheel or +/- keys zoom in and out.  Drag the mouse over the object with the left button moves it; with the right button (or control + the left button) rotates it.  On the Macintosh you can also open additional ObjView windows by dragging .obj files onto the application icon in the dock.  The mouse wheel zooms like the + and - keys.

One note: ObjView zooms in and out around the mouse, so you must point to the part of the object you want to see closer.  This can take some getting used to, but once you work this way you will find it to be a rapid way to move around the object, particularly if you have a scroll wheel mouse.

The 'c' key toggles back-face culling (the removal of hidden surfaces).  X-Plane always culls objects; if you turn culling off, you will see normally hidden faces tinted red.

The 'l' key toggles day vs. night lighting.  The 's' key toggles a solid or wire-frame view of the object.

Viewing Objects with Textures

To view textures in ObjView, drag a .bmp or .png file for the object's textures into the window that you want to view the object with.  ObjView does not pay attention to the relative paths of the bitmap file and object file; simply drag any properly named object and texture file into the same window to view the object with textures.

Note: on the Macintosh, textures are shared between all open ObjView windows.  This allows you to view multiple objects with a common texture easily, but you will not be able to view two objects with different textures of the same name.  For example, if a building from Boston uses the texture boston:wall.bmp and a building in Chicago uses the texture chicago:wall.bmp, you will not be able to view both objects at once because ObjView ignores the boston: or chicago: prefix and loads only the most recently specified wall.bmp image for both files.