User-oriented decentralised software distribution. Zero Install makes it easy for users to install software easily and without the need for root privileges. Drag a link from a program's web-page to add it to your desktop. Zero Install will automatically resolve dependencies, verify GPG signatures and check for updates.
The system is decentralised (there is no central repository), while still allowing libraries to be shared between programs. Secure hashes allow programs to be shared between mutually-untrusting users.