Lifehacker has a primer on Netcat, one useful utility which I don’t use nearly enough. Most stuff shown can be done with SSH, nmap, and telnet, but the author makes the point that netcat is on everything. So if you’re ever stuck without SSH, Netcat will be there. And if you haven’t setup passwordless logins for SSH yet, it’ll be quicker for many tasks than having to transfer keys around beforehand.