NixOS: purely functional system configuration management

> By not storing components such as libraries, header files or programs in
global locations, all packages are forced at build time to use a specific
version of their dependencies, located in the Nix store. To make this
happen, the developers have patched Glibc, GCC and the dynamic linker ld
to not search files in any default locations.

Something similar can be done also with scratchbox2 without a need to
patch Glibc, GCC & ld: http://packages.debian.org/squeeze/scratchbox2

(As it uses LD_PRELOAD, it works only for dynamically linked binaries or
scripts having dynamically linked interpreters.)