Last week, my entry to LD47 was an open-ended puzzle game (Zachtronic-style) where you construct a particle accelerator. You make particles speed up in loops and use collision chambers to create new and exciting particles! You can find the jam version here:
https://ldjam.com/events/ludum-dare/47/loopy-particle-simulator

I'm now working on a post-jam version, and the first release is here on itch.io:
https://nusan.itch.io/loopy-particle
This add: - save and load your creations (in freeplay mode) - improved performances with lots of particles (still not perfect) - add a "Panic button!" to destroy all particles in case of emergencies

Post screenshots of your circuits on the game page or on twitter @NuSan_fx as I would love to see them!