GNOME Power Manager is a GNOME session daemon that acts as a policy agent
on top of HAL (the Hardware Abstraction Layer).  GNOME Power Manager listens
for HAL events and responds with user-configurable reactions.
Currently it supports laptop batteries and AC adapters. Its goal is to be
architecture neutral and free of polling and other hacks.

WWW: http://www.gnome.org/projects/gnome-power-manager/