Debian/Ubuntu package which automatically enables a login console on a serial port.
This package spins up getty to allow login on serial console on ttyS0. Currently, it installs an upstart service that spins up getty on /dev/ttyS0. Install it and it does the rest.
Many servers provide access to a virtual serial port that can be accessed over a management network. An example is the virtual serial port available in HP's iLO. Many VM hyper-visors also provide access to a virtual serial port in the VMs. For example, libvirt can be configured to allow access to a VM's serial port by running "virsh console ".
Serial ports are everywhere and they are indespensible for those of us who like playing around with the network stack. Spin up getty and make sure you have a local user (not using LDAP or other network authentication service) and you have a way to get yourself out of any mistakes you make while configuring the network.