Atomic is a currency I worked on to develop and debug code that makes The Deck work. It was sort of a placeholder for colored coin currencies during development. It is an "atomic currency" and was needed as I debugged delegated fees and other aspects of indivisible colored coins.
After I made The Deck, I just kept Atomic in and bumped it from 100 coins to 10,000,000,000. It serves practically no purpose. It was "premined" into the coin company wallet and will probably sit for a long time. We may use it for promotions or an internal currency or not at all. It is not in competition with or has any influence on any other currency on the chain. It's perfectly benign.