NuBits is as stable as the USD. 1 NuBit = 1 USD, always, meaning NuBits are pegged to USD (Though there is discussion of pegging it to a different currency one day if needed).

People who don't live in the U.S can still us NuBits, just like people who don't live in Europe, can still use Euro. NuBits just acts as a way to digitally send money to someone using a currency that is pegged to the dollar.

If you have any more questions, you can ask them at the forums, which can be found at: http://discuss.nubits.com