In a logical world...

 I wondered whether you could make a world where as the creatures travel around they are really doing some sort of computation, even as they go about their daily business. One result of these thoughts was this weird virtual game world, made of critters traveling on a grid. Each critter can be either TRUE or FALSE: travelling east/west represents a FALSE state; travelling north/south represents a TRUE state. A critter goes straight until it hits either a NEGATION tile, which turns the critter 900 left or right, or an AND and OR tile. When a critter enters an AND or OR tile, the tile holds it there and waits for a second critter. Then the tile sends out both critters in opposite directions, either both TRUE (ie: heading north and south) or both FALSE (ie: heading east and west). Instructions are below.

Instructions:

• With your mouse over a tile, hit an arrow key to place a critter (use the DELETE key to remove it).
• With your mouse over a tile, hit '|' or '-' keys to set AND or OR. Hit ' ' to clear tile.
• Click on a tile to cycle through the four tile negation directions.
• Click on the STEP or RUN buttons to advance through a computation.

Source: test extends BufferedApplet