Hydra

 Hydra  either refers to a mythological many headed creature, or a W3C Community Group that aims to standardize how a web API can advertise its operations and what types of objects it expects/returns, or references to how they are related, paraphrased "Cut off one hydra discussion, Two more shall take its place.".

Wiki: http://www.w3.org/community/hydra/wiki/Main_Page

Spec Draft: http://www.hydra-cg.com/spec/latest/core/

Examples
No known real world examples of Hydra usage, certainly no selfdogfooding.

WSDL Again
The summary goal "aims to standardize how a web API can advertise its operations and what types of objects it expects/returns" is essentially the same as WSDL a failed effort to do the same.

Unclear what about Hydra is different (enough) to cause it to succeed where WSDL failed.