Tor is a simple, small and a free software by Tor Projects which helps you to prevent from surveillance that may harm your privacy. It acts like a proxy server and gives you total anonymity while browsing online.
It prevents anyone from learning your location and browsing habits. It is not just a web browser but a messaging client, remote logins and much more.
Tor Projects also provides a Tor Button which is just one click solution for Firefox users U click Tor Button and U get anonymous.