Wikipedia
NuBits are the worlds first distributed, stable value digital currency. One NuBit is equal to one US dollar in value. It works like many other popular digital currencies without the risk of volatility.
NuBits are notable for being the first decentralized cryptocurrency to maintain a $1.00 US price peg for a period of one year, having accomplished it on September 23, 2015. The Nu project is considered a global pioneer in the creation of decentralized stable-value cryptocurrencies.
Price is maintained by users placing huge market orders in both sides of 1 USD (or their equivalent in non USD exchange pairs), commonly refereed as sell and buy walls, to support the price within a narrow range of the 1 USD peg. The incentive to do so is the small commission between the market order and the 1 USD peg, usually <1%. Different users compete to be the closest price , so orders are filled with their walls and earn their profit, at the same time strengthening the 1 USD peg.
NuBits are the stable part of the Nu Network, the decentralized autonomous organization that started the project.