Short answers, pulled from the story.
The Denationalisation of Money, published in 1976, argues that private businesses should be allowed to issue their own competing currencies rather than governments holding a monopoly on money creation enforced through legal tender laws. Hayek contended that competition among private currencies would favor those with the greatest stability in value.
Hayek published the revised and enlarged edition in 1978 under the title Denationalisation of Money: The Argument Refined. In that edition, he speculated that markets would converge on one or a limited number of monetary standards rather than sustaining an unmanageable number of competing currencies.
Milton Friedman was critical of Hayek's monetary reform writings of the 1970s. He argued that Hayek, who championed invisible-hand evolution over central planning, was himself proposing to replace the evolved monetary system with a deliberately designed construct. Friedman also noted that existing law in most developed economies already permitted voluntary exchange via any mutually accepted medium.
In a 1977 review, Howard argued that Hayek neglected to account for how existing monetary institutions evolved to meet real economic needs. Howard also warned that a regime of competing private currencies might produce a new monopoly similar to the existing system, driven by the real costs and inefficiencies of running multiple currencies.
The European Central Bank identified The Denationalisation of Money: The Argument Refined as the theoretical root of bitcoin's decentralisation of money. Political philosopher Adam James Tebble has argued, however, that cryptocurrency takes decentralisation further than Hayek ever envisaged, replacing Hayek's vision of competing institutions with protocol-based issuance.
Economists George Selgin, Richard Timberlake, and Lawrence H. White have all cited Hayek's work on competitive private currencies. White, an Austrian School economist, was also a critic of Hayek's assumption that the most stable currencies would automatically win market acceptance.