The Best Remote Shell Program
Version to use: .57
PuTTY allows SSH connections to remote machines so you can get a system prompt. Plus, Simon is a pretty cool guy. I sent him an email with a question and he got back in a day or two with a reasonably helpful response, bless him.
Putty needs no installation, so some people like to use StartPutty.com to instantly run PuTTY on a machine that may not have it installed or in a place like a library where the computer may be locked down to a browser only, but if you can pull up StartPutty, you can probably run the program even with normal access to the machine.