Slackware's PackageManagement format.
These are simply TarBalls of the software, to be extracted in the filesystem root. They contain a desciption and postinstall script in /install, which are removed after successful installation. It doesn't get any more bare bones.
A large repository of Slackware packages is available at http://www.linuxpackages.net/.
You can use swaret or Slapt-Get to achieve dependency handling on Slackware much the way Debian's APT system works.