Maya Face Rigger
Here is tool I've developed that helps build the skeletal structures and accompanying controls for facial animation. It creates rigs that employ fully bone-based deformation, as opposed to morph targets or other forms of vertex animation. It is developed in Maya and scripted in Python. The model I used in this demonstration is the character TwinBlast from the title PARAGON. I owe thanks to the developers at Epic Games for releasing their assets, and to Kevin Lanning, the artist responsible for this character.
My goal while developing this tool was to package the intricate process of facial rigging into something more streamline and compact. While you can get impressive results with morph target animation, this tool works on any mesh without requiring an existing collection of blend shapes. It wraps Maya's bone creation and set driven key functionality into its own UI, so the user can focus on their creation. The general process on the user side is to select the portion of the mesh where they want a bone to influence, pick the new bone's parent, adjust the skinning values, and define a range of motion. The tool also allows joints to be represented by physical NURBS controls or as attributes in the channel box, so users can have control over how the space in their scene is occupied.
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Since the bone creation process leaves the range of motion specifics up to the user, there is little restriction on what types of features can be rigged. The same process works for muscles, eyelids, tongues, hair, etc.
This is a tool developed for those who know how facial rigs work, rather than a solution for people with no rigging experience. It requires some understanding of anatomy and motion to work effectively.