fdpowermon is a simple perl script that installs an icon in a system
tray compatible with the freedesktop.org specification.

Every three seconds, fdpowermon calls acpi to find out what the current
battery level is. It will set the output of the acpi command as a
tooltip text, and will update the used icon as appropriate.

In addition, fdpowermon can optionally call perl subroutines when the
power reaches a given level. No such subroutines are provided or
enabled by default, however.

Features:
- minimalist. The code consists of a good 500 lines, most of which are
  documentation and comments.
- A power monitor, not a power manager.
- The ability (not enabled by default) to suspend a laptop on low power
  levels, or do other tasks when the battery reaches a particular level.