This is a very basic engine for simulating stacks of crates.

The Game.as class shows a basic setup of the engine. You can give it access to a debugging graphic to see the internals working.

As much as one can criticise it for being so limited, that's the point. It runs fast, and objects don't pass through each other - it's not at all spongy, the units in this engine are solid bricks.

If there's any optimisations that could be further applied (other than a completely anal level of inlining), I would be very interested to hear of them as it would help future branches of this project a lot.