Best App in this category

It has a very good interface; a debt map, and a list of the countries where you click on them and see the real-time debt clock for that country and debt per-person (just by dividing the debt by total population).
This app may not be 100% accurate always as it takes a fixated rate at the time the data was updated, but it is taken from official government sources, according to the apps information. Either way, the rate it is stuck on until it is updated later on still acts as an accurate debt-clock.

I highly recommend this if you want to be aware of the worlds financial status.

Матвиенко about National Debt - USA & World, v7.4