Here is the prototype for the KGB booth game. It's hopefully fairly self explanatory: click to pick up or put down a piece, ctrl-click to delete it. Connect pieces using the gray ellipses. To drop a marble in, click on a blue marble.

Hopefully the pieces will be clear from playing with them; note that the first piece is a marble drop point; clicking the blue marble will drop one it. The last two pieces are intended as collectors. The numbered one is intended for a goal output, so you can see how many times you've one, while the unnumbered one is unnecessary, but avoids having dead ends. The remaining pieces are the available switches.

If you've got a game you like, you can (sort of) save it: clicking on Save should dump a lot of text into the textbox; this is the source of an SVG file. Just copy and paste it into a file with a .svg extension, and you should be able to open it up it and play it. I've made two games so far, an easier one and a hard one linked at the top (I believe the shortest solution to the hard one is eight steps.) Carolyn also contributed two... you should, too.

Finally, this seems to work as long as you don't try to break it, but is a giant mess of Javascript, and there are bugs. Sending multiple marbles through simultaneously generally works, but there may be some interesting race conditions, and making an infinite loop may break things. Also, I only tested with Firefox; I suspect Opera and Safari will also work, but that's just a guess. SVG is a fairly new format as far as browsers are concerned, so not too well supported.