Tools for Power Savings based on battery/AC status

 Laptop mode is a Linux kernel feature that allows your laptop to save
 considerable power, by allowing the hard drive to spin down for longer
 periods of time. This package contains the userland scripts that are
 needed to enable laptop mode.
 .
 It includes support for automatically enabling laptop mode when the
 computer is working on batteries. It also supports various other power
 management features, such as starting and stopping daemons depending on
 power mode, automatically hibernating if battery levels are too low, and
 adjusting terminal blanking and X11 screen blanking
 .
 laptop-mode-tools uses the Linux kernel's Laptop Mode feature and thus
 is also used on Desktops and Servers to conserve power