Localhost is a program that lets you access a shared, world-wide file system through your web browser. This file system is maintained in a fully decentralized way by all of the computers running Localhost. The program uses BitTorrent technology, and P2P Distributed Hashtable technology called Kademlia. (Localhost is a modification of Azureus.)

You can think of this program as one big shared network drive, built using BitTorrent so that it scales well and doesn't need a central server. You could also think of this program as a decentralized index for files distributed via BitTorrent; one that naturally evolves to keep the most popular files, and remove the unpopular ones. You could also think of it as a Wikipedia for files.