One of my duties as both a network admin and a consultant is to manage switches, routers and firewalls. Depending on the circumstances, establishing a telnet or SSH session to the device isn't always possible and a console connection has to be used.
For such serial communications, Windows comes with an app named Hyperterminal. Mac OS X doesn't come with an equivalent. A Shareware app named ZTerm ($20) is available and it certainly does the job, but an alternative named Minicom can do it for free.
Check out this article at AaronAdams.net to find out how to set up Minicom on your Mac.