Custom router firmware has (mostly) disappeared, mainly because Broadcom won't play nice and share its radio drivers with open-source developers. But that doesn't mean it's gone, and OpenWrt is still ...
So in this flat I have a fiber connection, with a PON. I plugged in my own Archer C6, flashed OpenWRT on it, and flubbed with configuration until I got it to work (I wasn't very familiar with OpenWRT, ...