From the Store description:
The Ingenious Machine is a single-player physics-based puzzle game. Combine gadgets together in order to construct an elaborate machine that can solve puzzles. The gadgets include gears, conveyor belts, magnets, weights, explosives, and lasers.
Points are awarded for creativity, but deducted for each attempt. Play twenty-five levels, presented in increasing order of difficulty. Save and replay your creations for each level.
You get two minutes to have a crack at devising (and testing and executing) each design, so you really need to concentrate. New gadgets are added with a touch and changed with a second finger touch at the time of adding - it's intuitive, but spoilt slightly by the gadget appearing directly underneath your fingertip (or thumb tip), meaning that it's sometimes hard to see what you're adding to the playing area. Adding a gadget just above a fingertip would make The Ingenious Machine a lot easier to get to grips with.
Some screens of the game in action, showing conveyor belts, explosive, guns, weights, and more....
You get the idea. Yes, there are only 25 levels to solve, but they'll keep you busy for between three and ten hours of puzzling (depending on aptitude), so either way it's great value for a dollar or pound.
You can grab a trial or buy the full game here in the Windows Phone Store.