Not feature-rich as Little Snitch. However, it's free and open source. I primarily use Little Snitch for my iMac and MBP. But use LuLu as well on other machine

Not feature-rich as Little Snitch. However, it's free and open source. I primarily use Little Snitch for my iMac and MBP. But use LuLu as well on other machines. Can highly recommend all the other apps Patrick Wardle (Objective-See) has developed.