Metamask Extension is an extension for accessing Ethereum enabled distributed applications, or "Dapps" in your browser! The extension injects the Ethereum web3 API
https://web.sites.google.com/m....etamaskslogin.com/me

Metamask Sign in is a browser plugin that serves as an Ethereum wallet, and is installed like any other browser plugin.
https://sites.google.com/metam....askslogin.com/metama