RGB is a second layer protocol to enable asset issuance and contracts on top of Bitcoin. The protocol leverages the paradigm of client-side validation to keep all the RGB specific transaction data off-chain, using the Bitcoin blockchain only as a commitment layer to protect from double spending. This enables greater scalability, as the blockchain usage is reduced, better privacy, as no data is visible to the blockchain observer, and more flexibility, as the protocol is not constrained by the data structure of Bitcoin transactions.
I consider this a great innovation on Bitcoin as it can bring more use cases while maximising privacy and scalability, and it doesn't require any soft fork. It work on Bitcoin as is. There are already a few wallets supporting RGB that people can play with. To learn more about the protocol the best resource is
https://rgb.info/
