http://www.portalprelude.com/
Portal: Prelude, as its name states it, is an unofficial prequel to the game Portal. Its story revolves around the pre-GlaDOS epoch, even before she was plugged in. At this time, test subjects were monitored by real Aperture Science employees whose work was tedious, lengthy and repetitive. This is why they decided to build a great artificial intelligence that could both replace them in these difficult tasks, but also take responsibility for many other tasks within the complex and compete with Black Mesa's superiority. All employees of the Aperture Science complex are now eagerly awaiting GlaDOS. Maybe even a little too eagerly, as the upcoming events will tell...
Trailer: http://www.ibisgaming.com/media/trailer.zip
http://www.steamfriends.com/mods/p2_articleid/1575
Yea that is right! The prelude to portal, death u better check it out too b/c I know that I am going to want those models for humans in lab outbreak
Here is direct DL link:
http://www.ibisgaming.com/media/portal-prelude-setup-1.0.0.exe
Here is the walkthough for the noobs that can not beat it:
http://www.portalprelude.com/walkthrough.php