The Pi side of the system is all OpenWRT with new packages created for things we need, like the custom linkmeterd that handles all the background HeaterMeter stuff. It is cut down to just be what we need so it can be as small as possible. Most of the "router" type stuff is removed, like firewall control, QoS, quotas, traffic logging, and just the stuff needed to be a client device remains. It is actually LEDE, because they broke off and took most the good development ideas with them so I converted from OpenWRT to LEDE. Now they're re-merged back to OpenWRT and I haven't had the time to re-sync with their tree.