Ethernut13G-Large
The Ethernut project site has source/shcematics for building your own OSS hardware /software embedded ethernet devices – “Ethernut is an Open Source Hardware and Software Project for building tiny Embedded Ethernet Devices… Three Open Source Reference Designs are currently available… The software is an Open Source implementation of a Real Time Operating System called Nut/OS and a TCP/IP protocol suite named Nut/Net. Several application examples are provided, including an embedded Webserver, a simple RS232 to TCP/IP gateway and an Internet Radio playing MP3 streams.” [via] – Link.

Related:
Other open source hardware projects – Link.