I used the Linux router, way back in '99 or so. Compiled onto a floppy and booted from that in read-only mode. It was a bit fussy about NICs and had no admin UI, but it worked. m0n0wall was good, but pfSense is truly gold-standard open source software, right up there with the best Linux distros, MySQL, the various Apache server products. I used to have a side business setting up and administering firewalls, routers, IPSec VPNs, captive portals, etc. for small businesses. Needless to say, pfSense was my go-to platform for most of that. I re-branded the web UI with my own logo and colors, so clients thought I was a real wizard.