The Machine is not, as you might expect, an Incredible Machine style game, despite the claim that it is "physics-based;" rather, it is a logic puzzle game. That is, there is really no opportunity for inventive solutions using Rube Goldberg-like mechanical contraptions that were not the designer's preferred solution (a specialty of Fantastic Contraption). Rather, there is a planned solution for each puzzle, and minor details of positioning will not (as they will in true physics games) defeat you.
The game is played in a square (or rather, cube) grid; you have to deliver some mixture of differently-colored and differently-sized cubes to one location in the grid. You place various items on the grid to 'fill the order,' some pre-placed by the level and some up to you to figure out how to place. You can remove and edit placements, and 'turn on' the mechanism to see what happens.
Manufactoria is obviously inspired by the idea of a Turing machine; in fact, the game almost is a Turing machine (it is not, because the tape can never be reversed in direction, and because symbols can only be written at the 'back' of the tape, not at any arbitrary position).
The conceit of the game is that you are building machines to test robots. Your machines consist of conveyor belts and logic gates, and 'robots' are spawned at one side of a square grid, and ones that "pass" must be delivered to the other.
Each "robot" is actually a linear tape printed with blue and red (later, green and yellow are added) dots. Each level has a different set of conditions; for instance, in the Robofish level, you must pass only robots with alternating blue and red dots; two of the same color fail. An unstated (but important) concern is that "no more dots" must be handled correctly -- in the Robofish level, it would mean "deliver this robot, but if the condition were "only first red", then it would fail.
From a programming perspective, one visual pun of the game is that a "loop" is literally that; if the "continue loop" condition is fulfilled, you want to build a loop of conveyor belts to bring the 'robot' back to the logic gate again.
One tricky feature (not stated in the game, at least that I noticed), critical beyond the first few levels, is that conveyors can "bridge" over each other; place the second level by holding shift as you place a conveyor.
In toto, Manufactoria is an excellent, brain-twisting puzzle game that, like the best, combines a few elements to spawn many possibilities -- no great surprise, given that we're in Turing territory here. It's also visually pretty dull, and the classical music is equally dull, but as a brain-teaser it has a lot to recommend.
TopHero is a small game -- just 8 levels, and likely less than an hour to complete them all. But it's an unusual one, and well conceived for what it is.
In each level, there is some sequence of hexes through which a hero must move to reach the level exit. You are a dungeonkeeper, and you have a variety of traps and monsters you can place in empty hexes; there may also be some hexes that assist the hero by healing him or providing new armor.
In Brent Anderson's Snowball's Chance, you play through a series of levels as a snowball. You start typically at one corner of the screen, and somewhere there's a goal you have to get to--sometimes by hitting switches and unlocking them first. The problem is that you don't move with the arrow keys; this game is somewhat billiards-like, in that you nudge your snowball with the mouse pointer, and can increase or decrease the force of your nudge. Some obstacles (like open water) cause insta-death, while wandering opponents can reduce your size. And you're slowly melting (more rapidly on some terrain than others), so you can't tarry.
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