BlenderDiplom stated a Halloween themed tutorial series to celebrate the season. The second part of the series has a look at using Blender’s Animation Nodes for target tracking. Frederik Steinmetz uses nodes to track the rotation of a few objects. The set up makes all the eyeballs in the scene follow a single object.
The setup can also control more than just rotation. It can control other attributes and effects as well.
If you are not familiar, Animation Nodes, like the name suggests, is a node based visual scripting system. The nodes add-on is designed to create motion graphics procedurally in blender.
Animation Nodes was an undertaking by developer Jacques Lucke. The Blender addon free to use, and comes with a wide range of nodes.