Counterparty is basically the extension we all were waiting for, or at least an attempt, from one of the biggest players in the network, Overstock. They are building an infrastructure on top of the blockchain that hopefully will make bitcoin the mean to transact in financial markets, like buying/selling stocks on their platform, Medici, which will be regulated by the SEC.
http://www.reddit.com/r/Bitcoin/comments/2mkd0o/we_are_the_founders_of_counterparty_the_free_and/
That should go under altcoin section
It's not an altcoin, they want to use Bitcoin's blockchain. Take a look at the project on the links you will find in the ama.