This one is fun to watch on a 3D display. (As much of it is black & white, anaglyph should also be worth a shot.)
Most of the effects could have plausibly been rasterised or blitted into a flat plane; alternatively, all of it could be done in a pixel shader which just colours in two triangles that fill the screen. But (as I discovered to my delight one day when I happened to have access to a Windows machine with a 3D monitor) it's all 3D geometry with a perspective projection.
For example, the wibbly-wobbly cone[0], viewed in 2D, could just as well be a flat bunch of sinusoidally gyrating discs all XORed together. But these discs are properly stacked along the Z axis.
The demo doesn't natively support stereo displays, so you have to find a tool that can inject itself into the graphics pipeline and modify the projection matrix for each eye. I don't remember which one I used when I tried that, but it had a nifty feature you should seek out: Hotkeys that let you adjust the mapping of depth to the stereoscopic shenanigans (separation and convergence) on the fly. Being able to make such tweaks on a scene-by-scene basis helps a lot with a production that was only designed for cyclops mode originally.
The same technique can be applied to many PC demos, but usually it only amplifies a 3D effect that was already there in the first place. In the case of Intrinsic Gravity, it gives you an extra dimension of 'whoa'.
Bonus recommendation for those who can't be bothered with any of that and just want to watch a neat recording on Youtube: Stargazer by Orb & Andromeda[1]. Nothing earth-shattering; just a personal favourite with a modern take on old-skool demoscene aesthetics and neat effects that don't fall apart in a video capture with limited bit rate.
[0] https://youtu.be/-ZxPhDC-r3w?t=67 [1] https://youtu.be/xgtghVdWlVY
http://www.wab.com - Have some amazing demos coded in Javascript and tutorials on how to create your own
http://modarchive.org/ - If your only interested in tracked music
http://www.pouet.net - A demoscene information source
HN's kiss of death may have crashed wab.com's server HDD.
Some of my demos:
https://tobireif.com/demos/swirls/
You can get pretty far making demo effects in CSS and JS these days. A couple of my attempts over on Codepen;
Text flash - https://codepen.io/onion2k/full/WyLoNg (Warning: flashing images)
Bitmap text wobble scroller - https://codepen.io/onion2k/full/rYgxdJ