Fantastic Contraption is a level-based physics puzzler reminiscent of, but far simpler, than the legendary Incredible Machine. In each level, you have to get your pink circle from its starting position into the pink "goal" area. Everything you build has to start within the blue "construction" area.
There are only five construction objects, but these suffice to create a surprising variety of devices using basic mechanical principles: wheels that rotate left, wheels that rotate right, wheels that are unpowered, rigid struts that cannot pass through other objects, and rigid struts ("water sticks") that can.
Because it relies on physics, there is no single, "correct" solution for any level; usually, a level can be solved in any number of different ways, with gizmos of varying complexity. Still, it's often non-trivial to figure out a solution, and the game has no hint system, which it could use; once you've solved a level, you can view other players' solutions, but not before, which may be an oversight. If you get stuck, I suggest looking at the game's forums--players can link to their own solutions, and actually, you needn't find one for your own particular puzzle. There are some basic techniques, such as bridge-builders and tractors, and once you get a sense of them, solving the puzzles becomes much easier.
There are only 20 levels in the free game, but $10 gets you access to more, along with a huge variety of player-created levels. (And there's a level editor, so you can create your own.)
It's interesting that such a limited suite of construction objects can support such a wide variety of puzzles, and it's nice to see a puzzler that relies on physics in an interesting way.