MakeHuman is a free facial expression system developed under open source. The software is still in development but already the results are impressive and the authors also updated their exporter so it can generate MHX Rigify checked character. For the macro-expressions the developers didn’t used Paul Ekman’s Facial Action Coding System which according do 2 facial actions a "merge" of the muscles that are in both the actions. Instead of this the authors developed a different type of actions that can be summed without problems in generic CG system.
In the new version the deformation are improved by adding extra bones to the deformation, in praxis it means that you can have control of the expression. The GUI changed also, it now offers slider to control specific areas of the face while the rest will change according to this changes. MakeHuman looks very promising and the showcase below will give you an idea how it works.
Source and full article: MakeHuman