Plone's related items functionality is a powerful feature but content managers mostly fail to do it (unless they are very committed and know their content very well). Here simserver comes to the rescue and assists in this task.
collective.simserver.related provides a form to query the simserver for
similar items and set them as related items. A simserver collection
queries the simserver for all documents related to this collection.
More information at: https://github.com/collective/collective.simserver.core