Portmaster

Portmaster is a free and open-source application firewall that does the heavy lifting for you. Restore privacy and take back control over all your computer's network activity. Discover everything that is happening on your computer. Expose every connection your applications make and detect evil ones. Finally get the power to act accordingly. Protect your whole computer, not just your browser. Block all advertisements and trackers for every application. Easily add your own rules and block individual domains. Make your own rules. Completely cut off applications from the Internet. Or block all p2p connections except for certain apps. Or never connect to specific countries. Portmaster has you covered.