In the united States. Article 1 Section 10 of the Constitution renders congress as the only power with ability to MINT coinage that’s used in US transaction. Currency (paper or electronic) you can legally do, although most fail several areas. In addition to the obvious problems of acceptance (banks and merchants) you also need a way to police counterfeiting. At the time of the foundation of the US secret service(1865) it is estimated that 1 in 3 bills in the US was fake. That’s a huge invisible tax on the general economy because if a dollar should be worth a dollar its really only then worth 67 cents because so many fakes drags down the value of the currency. Creation of souvenir coins not intended to act as currency, however, is not illegal.” – Quote from Laws Related to the Issuance and Form of Currencies.
Bitcoin (cryptocurrency) can be made (mined) at home, is widely popular, electronically based, but must be subject to taxes, and not a physical coin. You can buy a token or souvenir coin with the Bitcoin logo, but it is a novelty, not representative or linked in any way to the crypto currency. One unusual exception is the Casascius physical bitcoin, which had a chip implanted in it.
FYI, you can buy or mint actual Gold or silver coins, and they would be worth the value of the base metal, which can be in USD. Note the Elvis coins above.
You can use your coins as a method of exchange, based on their bullion or collectible value. For example, a 1oz Gold coin is pegged to the value of an ounce of gold. Please make sure you work with a lawyer on your team to make sure you are not breaking the law, by declaring your coin legal tender. If you do decide to make your own currency, as opposed to a novelty coin or souvenir/commemorative coin made out of a precious metal. (Note: I am not an attorney, this is just what I got from the web – my opinion does not constitute legal advice).
Good luck in your quest!
Disclaimer: I own Gold and silver coins. If you liked this, please repost and like!