Gargoyle is a front-end/web interface for OpenWrt, which is a free, open source firmware for routers.

Merlin is an upgraded version of the stock ASUS factory firmware for ASUS routers, with what appears (to my eye) to be a more polished user interface than most other router firmwares.

It is not fully open-source though, and includes (what I term to be) spyware from Trend Micro by default. I have removed those components from my own router.