I hacked this up over the last couple of days and the folks on #dsdev seemed to enjoy it, so I thought I'd link it here for your pleasure.
Note that the idea for the game isn't original; the code is mostly from a clone I made of the game by Dofi (written in Java, eugh).
The performance isn't great yet, but it's acceptable. The code will be released when I get around to dropping it on a version control system, under the GPL. There are a bunch more features I plan to add, including:
a title screen
more materials/combinations (steam, ash, snow, ideas welcome)
portrait view
a hideable toolbox instead of the arrow-key-selected icons
a way to stop/start the flow of individual sources