qconsole
http://jcs.org/

qconsole is a simple c application that makes an xterm window behave
like the console on the game "quake" (and probably many others).

when qconsole is started, it spawns an xterm with the "-into" option
to reparent it under qconsole, and then hides it offscreen.

to show the terminal, press control+o and it will scroll onto the
screen.  press it again and it will scroll back off the screen.  if
the xterm is killed, a new one will be spawned.

the xterm is launched with a name of qconsole.  to adjust its
colors and font, add xterm X resources to ~/.Xdefaults (and maybe
run xrdb) such as:

	.qconsole*background:           white
	.qconsole*foreground:           black
	.qconsole*internalBorder:       5
	.qconsole*utmpInhibit:          true
	.qconsole*rightScrollBar:       true

to adjust the window height, use the -h option.  to adjust the speed
that the console scrolls, use the -s option (1 to 10, default of 9).

if you don't like qconsole, there are a few other applications like
it that may work better:

visor (mac os x)
http://code.google.com/p/blacktree-visor/

yakuake (kde/konsole)
http://yakuake.kde.org/

guake (gnome/gterminal)
http://www.guake-terminal.org/