OpenWAN
From their site (with tweaks for readability)
The objective of our project is to provide FOSS (free / open source software) and more importantly Open Source Hardware solutions for those users who prefer the school of thought which says that the copper pairs or fiber that cross the walls of your castle and connect you to the outside Internet are of a distinctly non-Ethernet nature, typically carrying some HDLC encapsulation such as PPP or Frame Relay over some form of synchronous serial bit stream, and a highly competent network administrator at your site chooses his own WAN router to connect to this WAN interface in its native non-Ethernet form.
This is the traditional school of thought for T1/E1 and DS3/E3 connections, and one proud accomplishment of our project is that we've been able to extend this model to business SDSL as well.
Basically, these folks build open hardware for use in WAN-building.