Unity 5.3, 5.4 users please read the readme or check the forum.
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Module Generator is a multi-purpose random part generator.

It revolves around the Module component that gives game objects the ability to randomly and deterministically generate parts at specific attach points. Module creation is made easy by a powerful custom editor with prefab and undo support.

Different modes exist that let you decide when generation (and clearing) of parts should occur: on enable; according to the distance from an object (camera for example); by trigger collider; by the presence of an object within a zone; or by script. You can also generate parts directly from the inspector.

This asset is most useful to add some variation to existing assets, fully randomized objects, random level generation, culling and much more.