I second ce4's suggestion. LEDE/OpenWRT are open source projects of linux based firmwares that run on embedded devices. Tangentally, I've used OpenWRT in combi

I second ce4's suggestion. LEDE/OpenWRT are open source projects of linux based firmwares that run on embedded devices. Tangentally, I've used OpenWRT in combination with: a cheap router, a USB dongle as a second wifi interface, a 4G/LTE hotspot and a package called MWAN3 (previously MultiWAN) to configure a cheap and reliable setup for automated WAN failover (backup internet) and for circumventing restrictions of 4G/LTE hotspot devices.