Are you thinking of https://chir.ag/stuff/sand/ ? It was a Java applet I came across long ago via Fark from a Japanese forum. I really liked the concept but it was in a tiny 300x400 view. So I decompiled, resized it to be larger, recompiled, and have been hosting it at above URL since forever.

I tried to find the original dev but still haven’t found them. Of course with Java applets not working anymore, it’s just a relic of bygone times.