How do I create a hinged door that opens and closes in Blender? If I knew how to do this, then it would help me also create moving control surfaces on model aircraft, such as the rudder and horizontal stabilizers.
The easiest way (without rigging or armatures) is to displace the origin of the object on the edge you want to use as hinge.
Go to Edit mode and select the edge. Then press ShiftS to use the snap menu. Snap the cursor to selected.
In Object mode use Object->transform->Origin to 3D cursor. The origin of the object will be now on the edge of the door.
Rotate the object (in this case on the local Z axis).
For more complex objects or movements beyond local axis it's better to use bones and a rig.
Here is a picture of my scene.
The important parts the door, the door knob and the empty.
First I parented the door knob to the door. Select door knob then select door and press Ctrl P > Object.
Then I placed a empty at the location where the door hinge would be. Now parent the door to the empty.
The empty is now the controlling object for the door. Rotate the empty along the Z axis and the door and door knob will follow. You can lock the location, scale, and all rotation axes except for the Z axis of the empty. I added a Limit Rotation Constraint, so the door can't open into the wall.
Here I'm rotating the empty along the Z axis (note that the door does not open out even when rotated with positive numbers, because of the constraint.)