Anyone with a UNIX based machine (Linux or MAC) has access to a terminal. Anyone with a Linux computer has almost undoubtedly dabbled with command line utilities for some period of time. Here are a few little known terminal tools that I found interesting. I'll give examples of the tools, though it's worth noting that I'm on an Ubuntu Computer.
slurm: Displays network load using ascii art. slurm -i eth0
mtr: Traceroute on steroids. The kind the NCAA frowns on. mtr www.google.com
taskwarrior (package name: task): task add make todo list, task add relax feature rich console based todo list
nethack (package name: nethack-console): nethack For you truly hard core gamers a ascii art text based dungeon explorer move with the (h,j,k,l) keys open doors with o “?” for much needed help