www.aperturescience.com

https://valvearchive.com/web_archive/aperturescience.com/2007-10-17.html

You are presented with a blank terminal prompt.
You can do two things: LOGIN/LOGON/USER, which lets you log in, or you can type ?/HELP which will display a useless 'help' menu.

If you choose to log in, you can type any username that is greater than two characters, and use the password PORTAL or PORTALS or you can use Cave Johnson's account

Graffiti and pasted photos left by the Ratman in the Aperture Science Enrichment Center showing the login info for Cave Johnson's account.

When logging in, the visitor can also enter CJOHNSON as the login and TIER3 as the password, newly set as PORTAL ("CJOHNSON" refers to Cave Johnson, Aperture Science's CEO). These login and password can be found in Ratman scribblings spread around the Enrichment Center's maintenance area seen during Portal, with the words "trust me" right next to it.
After logging in as Cave Johnson, "GLaDOS v1.07a (c) 1982 Aperture Science, Inc." appears (it was originally "v1.07"). Then one can type either APPLY to start the test mentioned above, or NOTES, which will give information about Aperture Science and Johnson's history, in the form of a short timeline. The last paragraph of that timeline was later expanded and shown on Game Informer only, giving 1998 instead of the original "Several Years Later" as the date of both GLaDOS' activation and the Black Mesa Incident. While this new paragraph was written by Portal series' writer Erik Wolpaw, Half-Life series' writer Marc Laidlaw dismissed "1998" as the date for the Black Mesa Incident, as the date "200-" given when the first Half-Life was released is the only correct one.
The LIB command or any of its equivalents can still be executed; it will show all of the unusable commands and the new NOTES option.
INTERROGATE now works, except all names entered for the parameter are always responded with the error "Unknown Employee".
PLAY PORTAL will send the user to a YouTube video link. It has since been taken down by the user.

You are presented with a version string and yet another prompt, GlaDOS v1.07 (c) 1982 Aperture Science, Inc.
Here you can enter several things, with different results:
Command Result
THECAKEISALIE This is important! See the They Lied About the Cake section.
DIR/CATALOG/DIRECTORY/LIST/LS/CAT Lists the APPLY command.
IP Reveals your UID(+L) code. See the #UID section for more information.
HELP/LIB Lists the commands in this list.
LOGOUT/BYE/LOGOFF/VALVE Plays a sound and sends you to your homepage if you have one, or SteamPowered.com if you don't.
APPEND/ATTRIB/COPY/FORMAT/ERASE/RENAME Gives you an error about the disk being write protected.
INTERROGATE Gives an error if no parameter is provided, otherwise gives an error about 'illegally initiating diciplinary action'.
TAPEDISK Gives an error about the user not being authorized to transfer system tapes.
APPLY/APPLY.EXE Begins the registration process, before moving to stage three.
Anything else Gives an error about the file not being found.
Oddly enough, even though these commands emulate a DOS prompt, there is an LS command, which is from UNIX. Ironically, the actual webserver (this very server, to be exact) is running Debian.
Next you are presented with a Aperture Science notification. You can type CONTINUE or QUIT. Typing CONTINUE will lead you to another prompt.
Next you will be presented with a blinking UID, which starts as the same as you were given earlier if you typed IP at the prompt. The UID is irrelevant and has no use at this point in time. From here you can type CONTINUE or QUIT with an obvious result. Now you get to proceed to Stage Three, the questions!

Here you are asked a lot of weird questions, some revealing a few facts about what may happen during the game. You also learn a couple things about Aperture Science, Inc.'s weird obsession with cake. After you finish, proceed to Stage Four.
During this stage, a picture of a cake flashes at random intervals. According to a forum post on HL2.net there are numbers that flash on certain questions that spell THECAKEISALIE

The final stage! Basically they ask you to enter your case sensitive (read: it's in lowercase, you can only type uppercase) UID(+L). The fact that this is impossible is irrelevant, there is no code to continue past this stage. You automatically see the failure message.

An interesting message sent from someone who apparently 'hacked' into the terminal.

Originally posted by Web-site:

When was the last time you left the building?
Has anybody left the building lately?
I don't know why we're in lockdown. I don't know who's in charge.
I did find out a few things, like these terminals don't have to
tap out characters one at a time. And while we're all working
on twenty year old equipment, somehow they can afford to build
an 'Enrichment Center'. Check out this security feed.
Whatever the hell a 'relaxation vault' is, it
doesn't have any doors.

I don't think going home is part of our job description anymore.
If a supervisor walks by, press return!