I just found out about this a couple of days ago.
It's a small demo for Pathologic, that features a few different scenes in-engine. I don't know why it was made, exactly, but it's pretty cool. A nice way to revisit Pathologic if you haven't played it in a while
Or to see it for the first time if you've never played it(!)> Download screensaver (32 MB)
> You may also need this, if the sound doesn't work.
Run /Bin/Final/Game.exe to launch.
There's also a config program to choose your video settings.
Keys:
Space - change to different scene
F12 - screenshot
Alt-F4 - quit