I use Zenwalk, which is based on the Slackware distribution. It uses a one-app-for-one-task philosophy, default desktop environment is XFCE, although it's easy enough to use KDE, Gnome and Fluxbox on it. Lean and fast. They're switching to the gslapt system for updating their software packages (they have a central repository), currently use a script-based system called netpkg (which I rather like). You can install Slackware packages, too. Has all the libraries that a typical developer would like.