Developer: Hyperbolic Magnetism
Platforms: IOS Universal
Price: $3.99 (currently 50% off)
Let's get it out of the way now: Perfect Paths is clearly inspired by SpacChem. And as a mobile game, I feel that Perfect Paths is the superior experience. SpaceChem was a port; this was built from the ground up for IOS.
If you enjoyed SpaceChem and/or Trainyard, or like logic-based puzzles, you'll probably like Perfect Paths. It's challenging and tricky and satisfying and just a fun puzzle game.
You can purchase Perfect Paths for $1.99.