OpenWrt has a generic x86 PC build that can also be used to turn basically any random PC into a router, complete with an operating system actually designed and developed for that purpose.
OpenWRT is great if it fits your use case. If one has reason to stray from the happy path a disadvantage is that the OpenWRT uses a single binary like Busybox and doesn't use glibc. This is great for embedded/low power machines like the OG WRT54G, but not as optimal for when you have an entire random PC. I don't recall the exact things I was looking for but I moved on to pfSense and didn't look back.
Alpine Linux too.
And of course probably 1000x the power usage compared to the average off the shelf router that runs off a borderline microcontroller.