MetaMask is a free extension software available for Firefox, Opera, Google Chrome and the Brave browser. The idea is to create a bridge of information between Ethereum based dApps and your browser without the need to run an Ethereum node.
MetaMask also contains a security and identity interface allowing using to manage their online identity across various different sites. This interface also allows users to sign blockchain transactions.
Overall, the website is well polished and seems to have a high level of credibility. The identity of team members and founders are well presented right on the home page. Behind the professionalism of the site, one can tell this tool was created by real enthusiasts to bring Ethereum dApps to everyone and spread the joy of blockchain based technology around the globe.
Downloading the extension is made easy. Upon clicking the designated link for the website you’re using, you will be rerouted to the corresponding App Store.
The extension itself injects the Ethereum Web3 API into each website you visit to enable dApps the ability to read from the blockchain.
Every time a transaction on the blockchain is performed, MetaMask will open a security interface to review the transaction and decide which identity to sign it with.