Centralised crypto-coins are a digital asset built to be used as an item of trade. Additional crypto-coins are added via mining. Anyone is able to participate by using their a computer. Mining requires a lot of time and electrical energy, though. A powerful machine is also vital, to do this profitably. On the other hand, XRP is a centralised asset, which is unmineable. A fixed supply of units were created by the company and this limit will never be exceeded.