MetaMask is a bridge to Distributed web of tomorrow. It allows you to run Ethereum dApps right in your browser without running a full Ethereum node.

MetaMask includes a secure identity vault, provides user interface to manage your identities on different sites and sign blockchain transactions.

You can install MetaMask add-on in Chrome, Firefox, Opera, and Brave browser.
MetaMask for Chrome
Metamask for FireFox
MetaMask for Opera