Quake II In Full Motion Stereogram 3D Engine
crhylove writes "A guy called Lewey Geselowitz has hacked the GPL Quake II code to display a real time full motion stereogram SIRD 3D environment. Warning, though, it's very hard to play if you aren't excellent at focusing on SIRDS already. He has a download page on his personal site with more information." The page notes: "You finally saw the yacht in the seemingly random bunch of dots! Now use your skills to free yourself from your evil extra-dimensional zombie oppressors! Welcome to Quake II as it was never meant to be."
This isn't exactly new in a game... I remember that Bullfrog's Magic Carpet had this feature way back in 1994. It was virtually impossible to actually play while in this mode, of course, but it was kind of neat for a few seconds. But it was nothing more than a gimmick: certainly not a major feature.
While Quake II would be even neater, I don't think anything's changed now... Hell, text-mode Quake II would be more playable.
This article gives a nice overview of how Single Image Random Dot Stereograms (SIRDS) work and their history.
Also, check out this Java applet here which can generate stereograms, with source code.
Grab the Quake 2 demo from GamersHell, install it and replace ref_soft.dll with the AbSIRD one.