Ripple (RPX) is a bit odd in the world of altcoins. It had been around as an open source project for a long time, until a company was launched, a zillion coins were premined. Bitstamp supports Ripple. Switching costs are pretty low, but the cost of supporting more infrastructure in parallel is non-zero (and is bigger the more the different the system is, which is why Ripple isn't making headway).
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