Procedurally generate characters using tools similar to those found in The Sims, Saint's Row, makehuman.org and Mixamo's new "Fuse".
Body types can be generated by blending in different attributes, like sex, height, muscle & fat. Face structure can be customized using attributes like mouth width, eye spacing, forehead height, etc. However, customization tools can go beyond this by utilizing many of Houdini's built in tools.
Skeleton & generated mesh can be exported in formats that are compatable with packages and services like Unity or Maya.
MakeHuman (open source)
SIMS - character creation walkthrough