Network UPS Tools is a suite of programs that can be used to monitor
the status of an Uninterruptible Power Supply.  Nut tries to support
"every kind of UPS with sufficient interest behind it."  Most decent
UPSs have a serial port for access to status information.  The primary
use of Nut is to notify the machine in the event of a power failure so
that scripts may be run to properly shutdown your machine.  Nut also
has a network communications layer that allows other machines to
coordinate shutdowns with the machine that is physically attached to
the UPS.