There's a modified version kicking around now, too:
http://fallingsandgame.com/sand/sand.html
New/Different stuff:
-"Zombies": Little floppy things that pretty much just sit there. Haven't found any practical use for these yet.
-"Hand": For moving the Zombies
-"Snig": replaces the yellow blobby thing from the original. Seems to be a little more rigid than the other thing. Still grows with water and shrinks/dies with salt, though.
-New interactions with water and the three other particles. Sand sinks to the bottom of water, oil floats on water, and salt is absorbed by water. Salt water particles don't have any interactions with anything that I can tell. Plants wont grow in them, and none of the other particles react with it at all.
Another thing that I haven't seen mentioned before is that Sand eats through Spout, but in a weird way. Instead of just dissolving it or something, it actually turns the Spout into Sand, similar to how the Plant grows in water.