What is Shadow on Solana?

Could you please explain what exactly is meant by 'Shadow on Solana'? Is it a new cryptocurrency or a service built on the Solana blockchain? How does it differ from other projects on the Solana ecosystem? What are its main features and what problems does it aim to solve? Is it a decentralized application, a protocol, or something else entirely? And finally, how can potential users or investors get involved with Shadow on Solana?