This is an chrome extension,which allows us to communicate with the etherium Blockchain, to send or receive ERC20 tokens from our one account to another account. It saves the passwords and secret information of our accounts in our browser as a local file and that information never touches the MetaMask servers or the Etherium Blockchain.The best thing about this wallet is that you can set your own currency i.e your own coin. you can send it to your other accounts as well.
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From @cryptozert