Gargoyle: completely open source and easy to use

OpenWrt builds on x86 so Gargoyle does as well, in fact they have an x86 device image as a download. You might have to build from source to get your hardware supported. Then just run it on your gateway as the bare metal distro. Odds are anything you already run on your gateway is in the OpenWrt repos if they aren't in Gargoyle's. Pretty much anything you would imagine running on a router/gateway/firewall/bastion is there and a lot you wouldn't (multimedia, X, etc).