Centralised cryptocurrency is a code-based asset built to work as an item of exchange. Additional coins are found via mining. Anyone can get involved if they have a a computer. Mining uses a large amount of hours and electrical power, however. A high-powered machine is also needed, to mine profitably. On the other hand, Ripple is a centralised asset, which can't be mined. A limited supply of units were generated by the organisation and this number will never be exceeded.