We use Conserver, the "console server daemon", to manage serial consoles for most of our systems. Several systems can be powered on using the serial console, and the others are useful for the accessing the system when the network is misconfigured or down.
To get a list of consoles, type "console -x":
% console -x Enter hobo@caffeine's password: ascorbic-acid on /dev/ttyS0 at 9600n potassium-citrate on /dev/ttyS1 at 115200n citric-acid on /dev/ttyS1 at 9600n [...]
To connect to a console, type "console <name>", replacing name by the name of the console.
% console caffeine Enter hobo@caffeine's password: [Enter `^Ec?' for help] Debian GNU/Linux 4.0 caffeine ttyS0 caffeine login: