I've this in my drawer for a while:
The thing is a high precision rubidium frequency standard. It is like an "atomic clock" just it uses rubidium instead of cesium.
The DB-9 connector on it not just for the power source and the 10MHz output, but if I'm lucky and this model is capable (according to the ebay seller, it is) to program it between 1Hz and 20MHz.
I think, instead of just using this as a 10MHz standard, I'll put an MCU next to it with a display and some control switches/buttons. As the result I'll get precise variable frequency standard what can provide output in the frequency range mentioned above.