Multi-user and multi-aplication (different applications can depend on different versions of a shared library).

Here's another example that's not public, and not really a distro, but... http://stackoverflow.com/questions/3380795/what-does-amazon-...

GoboLinux works in a very similar manner, though I'm not sure the distro has seen any love in a few years.

I've read dpkg has `dpkg -i --force-not-root --root=$HOME/.local package.deb` options, but I haven't ever tried those myself.