Meet Laureline. Given only a GPS antenna, a power source, and a clear view of the sky she can track UTC to within 200 nanoseconds and make precise time available to your entire LAN, WAN, or to the Internet.
Laureline is open-source hardware, provided under the Creative Commons Attribution 3.0 license. It was developed using Altium Designer but a PDF of the schematic as well as the Gerber and NC Drill outputs is provided below. The current hardware revision number is 7.