“Rather than trying to bootstrap an entirely new blockchain, as every other cryptocurrency does, Mastercoin seeks to create an entirely new network of currencies, commodities and securities on top of Bitcoin itself. Today, one mastercoin is worth about 0.1-0.3 BTC, over ten times its original BTC price at the timeof the fundraiser, and twenty times its original USD price. Why has Mastercoin seen so much attention? Essentially, the main attraction of Mastercoin is the sheer number and depth of the features that it brings. The following is a sample of what the Mastercoin specification intends for Mastercoin to support.”
http://bitcoinmagazine.com/7961/mastercoin-a-second-generation-protocol-on-the-bitcoin-blockchain/
rather than trying to bootstrap an entirely new blockchain, as every other cryptocurrency does, Mastercoin seeks to create an entirely new network of currencies, commodities and securities on top of Bitcoin itself.