Instalation

Installing Rigged system is simple:
Download the file
Unzip the zip file, then you will get a new zip file and a blend file.
Select: File → User Preferences ... → Add-ons from the menu
Click ‘Install from file …’ (at the bottom of the screen) and select the zip file: Rigged systems rev 1  zip file
Click ‘Install from file ...’ (at the top right of the screen)
Check the enable check box to the left of the add-on you just installed

Installing an updated version of Rigged systems

If you want to replace a previous version of Rigged Systems you have to remove the old version first. to do this, go to File → User preferences … → Add-ons and either search for IDMapper or go to the ‘3D View, TOOLS’ category where it will be located. Click on the add-on and then on the ‘Remove’ button. After removing the old version follow the instructions above to install the new version.

Setup

• Point the folder "File location:" to where the file Rigged_Systems.blend i located.

Blender 2.8 update
The addon have got the same functions as below but the addon is located in the right meny in the "misc" folder. Also since Blender 2.8 no longer have got "Groups" the differnt riggs are imported to a "Collection" instead. The differnt emptys that are added is located under the collection called "Added_Emptys"

Functions in object mode:
Cursor to object mesh - place your cursor in the middle of selected object.
Empty - Plain Axis to object 0.2 - place an empty with size 0.2 in the middle of selected object.
Selection to selected - Takes the first selected obejct and place it in the same position as the last selected object.
Selection to selected and copy rotation - Takes the first selected obejct and place it in the same position as the last selected object and also copy the last selected obejcts rotation.

Add rotating axis - Adds an empty that can be rotated around X-axis. Follow the 3 steps below
       Set start point to roating axis - Selected object where the axis should be located.
       Set direction to rotating axis - Select object in which direction to X-axis should go.
       Make rotating axis - Finaly makes the axis.

Add Cylinder Rigg - Adds the rigg for rigging a cylinder
Add Turnbuckle Rigg - Adds the rigg for rigging a turnbuckle
Add Universal Joint Rigg - Adds the rigg for rigging a Universal Joint
Add One Wheel Axle Rigg - Adds a axle with two wheels. Move the empty in Y-direction and the wheels                                                 turn. (This is a simple wheel rigg and can not be used for advanced rigging)
Add Tank Tracks - Adds the rigg for simple tanks tracks that moves in X-direction (This is a simple rigg                                                 where it only works in the X-direction and nothing more.)

Functions in edit mode:
Empty to object edit mode 0.2 - place an empty with size 0.2 in the middle of selected object.

Add rotating axis - Adds an empty that can be rotated around X-axis. Follow the 3 steps below
       Set start point to roating axis - Selected vertexes where the axis should be located.
       Set direction to rotating axis - Select vertexest in which direction to X-axis should go.
       Make rotating axis - Finaly makes the axis.

Update 2020-05-03 and only for Blender  2.8x

Empty to face  - Adds an empty to slected face in edit mode, The empty will have the Z- axis in the normal to the face selected.

Face to X direction  - The selected object will have the selected surface in edit mode oriented in the positive X axis.

Face to Y direction  - The selected object will have the selected surface in edit mode oriented in the positive Y axis.

Face to Z direction  - The selected object will have the selected surface in edit mode oriented in the positive Z axis.

Link to videos below for each seperate function: