telnet
Originally a Unix command now used by a lot of OSs. Basically an unsecure way to access another computer. Usage 'telnet slothmud.org 6101' but if you hit enter after typing telnet, its 'open slothmud.org'
There are many enhanced 3rd party telnet widgets out there, like TinTin or wintin if you need alias scripting etc.
If you need to get by a firewall, make sure you have the telnet port open(port 23), or the port number specified, as in 6101 in my example above.
If you can't see text or are having weird format problems - check your display properties in telnet...i.e. Terminal Type (vt100, local cursor echo etc..)while in telnet, use '?' for options(XP), and Winblowz 95/98 have a options box for terminal type, machine, and port.
Use SSH for ecure connections.