There is plenty of remarkable work being done over at Dofi-Blog with both the Java and Processing languages. Although the blog is written predominantly in Japanese, there are at least a couple of engaging interactive games and toys that should not be missed regardless of your language of choice.
The first is a Java-based applet called War of the Hell. And while I am not sure why the author chose that title, I am almost certain the game was loosely inspired by a short story of famous Japanese writer Akutagawa Ryûnosuke. In The Spider's Thread, Buddah rescues an evil man from Hell—a man who had performed a single good deed in his lifetime—by using the thread of a spider's web. A spider's thread was used because the man had once spared a spider its life by choosing not to step on it.
In the game, you control a highly elastic string and attempt to fling the souls that cling to the string up towards Heaven. There is no time limit, just a counter that keeps track of how many you save, and the maximum number of souls you save in a single chain. Very impressive.
This next fascinating interactive toy was created with the Processing multimedia language. It involves playing with sand, water, salt, and oil as molecules of each fall from above. Use the mouse to draw walls for the materials to flow over and around. Ignite the play field with fire or a devastating(???) explosion. After allowing it to run for a while I noticed that the ball of sand grew bigger as it collected the materials that poured over it.
There is no point to it really (and why should there be?), and yet there is plenty to do and to discover with it. The ball of sand seems to be affected differently by each of the falling materials. There is more here than I can discern on just a casual glance.
The name of the piece is World of Sand (with thanks to Sariko for the translation =) The babelfish translation of the title is "The Licking World" ...or something of the sort, which had me rather confused. All I can say is try it. You will be, at the very least, intrigued by its interactivity.
Thanks to Lee for the link. =)
Looking for more sandbox fun? Try Hell of Sand, or Sand, Sand, Sand, both are newer updates to the ones posted here.