Rewrite of the normalisation engine. Multiple builds can now be performed in parallel (option -j). Distributed builds. Nix can now call a shell script to forward builds to Nix installations on remote machines, which may or may not be of the same platform type. Option --fallback allows recovery from broken substitutes. Option --keep-going causes building of other (unaffected) derivations to continue if one failed. Improvements to the garbage collector (i.e., it should actually work now). Setuid Nix installations allow a Nix store to be shared among multiple users. Substitute registration is much faster now. A utility nix-build to build a Nix expression and create a symlink to the result int the current directory; useful for testing Nix derivations. Manual updates. nix-env changes: Derivations for other platforms are filtered out (which can be overridden using --system-filter). --install by default now uninstall previous derivations with the same name. --upgrade allows upgrading to a specific version. New operation --delete-generations to remove profile generations (necessary for effective garbage collection). Nicer output (sorted, columnised). More sensible verbosity levels all around (builder output is now shown always, unless -Q is given). Nix expression language changes: New language construct: with E1; E2 brings all attributes defined in the attribute set E1 in scope in E2. Added a map function. Various new operators (e.g., string concatenation). Expression evaluation is much faster. An Emacs mode for editing Nix expressions (with syntax highlighting and indentation) has been added. Many bug fixes.