What is Numeraire NMR?

Could you please elaborate on what exactly Numeraire NMR is? I understand it's related to cryptocurrency and finance, but what specific role does it play in this realm? Is it a token, a protocol, or something else entirely? How does it differ from other cryptocurrencies in the market? What are some of its key features and advantages that make it stand out? Additionally, what are the potential risks and challenges associated with investing in NMR? Thank you for your insight.