In my previous college class, I was shown an OS called Tsurugi. Tsurugi can be downloaded from their main page at https://tsurugi-linux.org. It is named after a legenary Japanese double-bladed sword used by ancient monks which might be something similar to the image below.
pfsense probably is the most well-known used used open-sourced Linux firewall appliance in used today. It provides an easy to use web page GUI and installation is extremely easy.
