It was designed to allow a client to run code submitted by other clients safely on the browser without isolated environments. It is an important building block for a decentralized-application browser I'm developing. In the soon future, you will be able to publish a decentralized application with an one-line command. It will be stored on Swarm (decentralized Store), will use Ethereum as the back-end, and anyone will be able to access it using a decentralized browser such as Mist.
So, in short, remember the Pirate Bay idea of putting drones around the world to host their sites, allowing it to stay up forever without censure? Moon does exactly that, without the drones of course.
There is no competition to Ethereum in terms of back-end decentralized computer, AFAIK. I picked Swarm because of familiarity and being closer to the devs. I don't know the IPFS devs. I do find both projects awesome.
