Bitcoin, dogecoin, ethereum and other cryptocurrencies are similar to digital gold. The algorithm to generate a cryptocurrency can be downloaded from developer websites. It is theoretically available for everyone to use in creating new currencies. However, the competition is fierce because there is a limit to the number of coins that can be circulated. This limit varies depending on which cryptocurrency you choose and is set by the person who created it. The bitcoin algorithm, for instance, limits how many bitcoin can be created to 21,000,000. After that, there will be no further bitcoins.