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Any more details about the game itself? Because I'm just thinking of Audiosurf, but as I've never played it, I don't know how big the download is. All I know is that it is indeed 3D and gameplay is loosely based around sound and color.
No, this is a mostly visual game. I remember that all the player really does is walk around. It was also a completely free game. I think it was freeware, but I'm having trouble finding it on the freeware game list here. This would be in the same vein as LSD: Dream Emulator.
Also, character is AFGNCAAP.
What kind of places did you explore in the game?
Is it possibly The Endless Forest?
Online game to download and play. Basically only visual and auditory, with no real meaning or storyline. 3D. I remember seeing it on TV Tropes but I could be wrong. The dl file is about 1 Gig if I remember correctly.