I designed a precision timebase for my clock projects. As it turns out a friend was intrigued by the idea, since he needed a precision timebase to count cell devision time in cancer research. Therefore short and long term stability is needed. Their approach was to use an OCXO and a Xilinx FPGA.

By using the pulse output of a GPS timing module (uBlox M8F) to drive a mu-processor (Atmel XMega) at 20 or 30.72 MHz a very precise time base can be generated. Short term is given by an VCTCOX and long-term stability by using GPS time. This ensures time measurement of 5ppb with GPS locked and 100ppb/24h hold over.
This timebase has a wide field of applications ranging from biology, physics, etc.
The whole timing module (GPS-antenna, GPS receiver and u-Processor) range at at about $200, making this a real alternative to a used rubidium oscillator.