LuLu is a smart, free and open-source firewall for macOS. It blocks the internet connections for any new and unknown apps running on your Mac. It allows all the Apple programs to connect to the internet so that the system is not overburdened by the firewall activity. But when you try to run a newly downloaded or installed app, it will block that app and seek your permission before letting that app connect to the internet.
Installation of the LuLu requires that you restart your Mac and allow it to control your system in the system preferences. It places an icon in the system status bar using which we can disable the firewall if needed. For example, if it is causing too many alerts during the installation of a software then we can disable it for a few minutes.
In the LuLu rules we can allow all Apple programs to access the internet after which no matter their location, all programs that are digitally signed by Apple will be allowed. We can also allow all the apps and programs that were already installed on our Mac before we installed LuLu firewall which makes sense because it is going to save a ton of time which other we would have to spend configuring all the different apps in the firewall.
LuLu can be run in active or passive modes. In the active mode, we see all the alerts and it seeks our permission whether to allow or block a new unknown app. In the passive mode, it runs silently without any alerts and allows any new connections automatically. There is an option to hide the icon from the status bar.
LuLu blocks only outgoing connections and it does not prevent any incoming connections. This makes things much simpler can keeps the firewall lightweight. This is why LuLu is so lightweight unlike some other similar software designed for Mac. It is very helpful in preventing any unknown apps that could be leaking your personal data without your knowledge.
You can download LuLu firewall for macOS from https://github.com/objective-see/LuLu.