<A target="_blank" href="http://www.cio.com.au/article/380396/google_releases_open_source_bitcoin_client/">BitcoinJ, developed by Google engineer Gavin Andresen,</A> implements a "simplified payment verification" mode that doesn't require a central bank or payment system. <A target="_blank" href="http://www.weusecoins.com/">This is a short video explaining how the system works.</A>