What is Mastercoin/Omni?
Omni uses the Bitcoin’s blockchain to store records and data and allows users to create their own digital tokens and by that creating smart properties. It is intended to be a base upon which anyone can build their own currency. The Mastercoin/Omni project officially launched on July 31, 2013, with a month-long fundraiser in which anyone could buy Mastercoins.

Features of Omni
The primary features of the Omni layer are different ways for user to create their own custom currencies straight from the client. The new user currencies include a variety of different use case, including Smart Property, Pegged currencies (e.g. pegged to the value of Gold), and Decentralized Applications where tokens include not just a financial aspect, but also decision making power.
Second-Generation Protocol on the Bitcoin Blockchain
The key difference in Mastercoin is this: rather than trying to bootstrap an entirely new blockchain, Omni seeks to create an entirely new network on top of Bitcoin itself. The Omni protocol layer mediates between the existing bitcoin protocol and users-generated currencies.