The mobile network
When I took my laptop to different locations within our company building I always had to reconfigure the network, or shut it down and boot it back up at the new location. Then, I found this little daemon at https://www.stud.uni-hamburg.de/users/lennart/projects/ifplugd which waits for link down and link up status changes on a network device and can execute any actions on these events. On Debian, a simple “apt-get install ifplugd” was sufficient so that the laptop now reconfigures the network device when the link has gone down and comes up again.