Centralised crypto is a digital asset created to be used as an item of exchange. New units can be added through mining. Anyone can participate if they've access to a computer. Mining uses a large amount of time and electricity, however. A fast computer is also needed, to do this profitably. Conversely, Ripple is a centralised coin, which is unmineable. A finite number of tokens were generated by the firm and this number will never be exceeded.