OpenSnitch
OpenSnitch is a GNU/Linux port of the Little Snitch firewall
...Once you know which are the common processes, IPs and hosts that your machine is connecting to, you can start creating permanent rules (Duration: always) to deny or allow them. You can also convert temporary rules to permanent by right-clicking on a temporary rule or by double-clicking on it, and then edit it. By default OpenSnitch UI listens on a local Unix socket in /tmp/osui.sock.