bitUSD, bitEUR, bitBTC, bitGOLD etc are smartcoins on the Bitshares blockchain. They are price-stable coins that maintain their price by being backed by at least 1.75 times their worth in BTS (Bitshares). They are shorted into existance by Bitshares users and the users’ BTS are locked as collateral. You can read this in more detail in the following post:
OPEN.BTC on the other hand is an asset issued by OpenLedger (which is a company that also provides a gateway for Bitshares). OPEN.BTC is an IOU for BTC. This means for every OPEN.BTC that you have, OpenLedger promises to give you 1 BTC upon withdrawal. This is a great feature that lets you trade and keep BTC and other cryptocurrencies like Ethereum and Lisk on the Bitshares blockchain.
You can deposit BTC to your Bitshares account using the deposit feature provided by Openledger. This will give you an equivalent amount of OPEN.BTC on the Bitshares exchange which you can transfer/trade using the awesome blockchain that processes transactions in 3 seconds instead of 10 minutes. Then later if you want to withdraw your BTC, you can use the Withdraw option to withdraw your OPEN.BTC back to your Bitcoin wallet in BTC.
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