With the quality of entries I've seen so far, I don't like my chances of winning, but it would be nice to get a badge!
I'm going to use this contest as an excuse to redo a previous model of mine - a GBC module powered by pneumatics. This is what the old version looked like:
I have used it in a previous display, but it has numerous shortcomings as a GBC module.
The output is not in line with the input, violating the spec. It was what I needed at the time, but it's not suitable for general use.
The output is impolitely high. Again, it was what I needed at the time, but I couldn't put this into a normal circuit.
It would frequently jam.
It spilled lots of balls.
I will be using the same sequencing (basically the simplest alternating sequence possible). I had toyed with the idea of something more complicated, but 1) I couldn't get my head around how to make the sequence I wanted, and 2) it would have been too slow anyway.
I probably won't make a compressor for this one, leaving it hand-operated. The idea being that in a display it can be somewhat interactive - the audience gets to power the Contraption (or at least some portion of it).
Best of luck to all entrants!