Arrange your elements so that the initial toppling of the starting block causes a chain reaction that triggers the raising of a flag at the other end of the screen. After laying everything out press the "Play" button and then click the first block to set your Goldbergian contraption in motion. You have more blocks, balloons, bowling balls, and even a nuclear blast at your disposal to complete each stage.
There's a good handful of default stages included in the game, but a level editor with cut and paste codes allows you to create and share your custom stages for a real sadistic challenge.
Analysis: Sky Blocs is a great puzzle game in the tradition of The Incredible Machine, and it's just as addictive. The domino-like blocks being the main element makes the game that much more intuitive, since the physics of toppling dominoes is almost universal knowledge. It's very easy to look at the stage, look at the elements you have at your disposal, and begin to imagine a successful layout.
Easy to imagine, but not always easy to accomplish. The included levels are suitably difficult, though some I found relied more on size and repetition for their challenge rather than cleverness in design. Hey, that's what the custom levels are for, right?
One minor problem I had was the counter-intuitiveness of the starting block. Rather than clicking on the opposite side of the direction in which you want it to go (simulating the "flick" of a finger on a domino) you click on the the same side. It's small but annoying, something I kept occasionally doing wrong even after 9 levels or so. Maybe I'm just not that bright!
I also felt that for a game based on toppling dominoes, Tom missed the mark on one major design choice: speed. Most of the fun of watching a string of dominoes fall is the combination of the blur of motion and "clackety clack" of the bones hitting each other. What Sky Blocs really needed was to be greatly sped up, or at least offer a speed option.
Other than that I thoroughly enjoyed wracking my brain over each increasingly more challenging stage.
An updated version of the game is available to play at Tom's The First Door site.