Nxt is considered a 2nd generation crypto currency. With all the alt coins that alter parametes such as hashing mechanism, time between blocks, starting difficulty, and so on, Nxt brings much much more to the table and was designed this way for a number of reasons. It's proof of stake model makes it less susceptible to 51% attacks whilst it is designed to support large transaction volumes, something which the traditional Bitcoin and its clones have as a potential flaw. Nxt allows the creation and exchange of custom tokens, coloured coins and assets on the Blockchain.