Nouns are pseudo-randomly generated using the previous block hash as the seed to determine traits. Synthetic Nouns are pseudo-randomly generated using your Ethereum wallet address as the seed. Each wallet can only generate one Synthetic Noun, and there are over five million combinations.
Concept inspired/borrowed from Dominik Hofmann Synthetic Loot project.
Contracts are currently deployed on Rinkeby to serve purpose. Anyone is free to deploy them on main-net.