Interesting game, played through what is there so far. The sand physics is fun, the components to build from feel fitting together well to create interesting and functional contraptions. What I imagine would be challenging is to make the game mechanics (sand physics) fast enough for a solid, smoothly going game, it struggles a fair bit already for the later goals (was playing on Chromium).
Hey! (Didn't see the reply until now.) It's all JavaScript. The biggest problem is that I can't share arbitrary memory between threads so I have this convoluted solution that would be completely unnecessary in other languages. The simulation wouldn't be possible without multithreading so it's kind of frustrating but still fun to work on!