Non-biped setups — a kraken, an eagle and a Chinese dragon — where the deformation problem changes with every anatomy.
Creature work is where generic rigging solutions stop being enough. A kraken needs many tentacles that all move as continuous, flexible curves; a wing needs a skeleton that folds and spreads like the real thing; a dragon needs a long spine that reads as one continuous motion.
I used the ribbon IK method to procedurally generate the rig for every tentacle, and that work eventually became the Ribbon IK Plugin.
Built for a semester-long school project. It got me familiar with animal rigs, especially how bird wings work and how to achieve that behaviour with a skeleton.