Money provides such a significant advantage over barter in an economy, that it is indispensable for a functioning economy in today's world. Modern civilization has been accustomed to a government or pseudo-government entity creating and maintaining a money supply. Indeed, these currencies have dominated the economy across the globe throughout living memory. Recently, cryptocurrencies have been on the rise, but they are far from replacing dollars, pounds, and yuan. In a truly free society, how would money be provided for the economy?
In short, it would be provided the same way all goods and services are provided in a free society: by mutually voluntary human interactions in the market. Without a government-mandated currency, printed with a legal obligation to accept it in payment of debts, people would be free to produce or accept any currencies they choose.
Governments are typically opposed to currencies that can compete with their own. China recently prohibited ICOs. The U.S. is prosecuting men for selling Bitcoin. Bernard von Nothaus got off with a fairly light sentence after being accused of domestic terrorism for his Liberty Dollar alternative currency. Jonathan May was imprisoned for years for attempting to create a non-fractional reserve alternative to the Federal Reserve. In a free society, all cryptocurrencies would be free to compete on the open market with privately manufactured specie and paper instruments.