Invisible Enemy is a set of free wargames rules with an interesting premise: that in the future, tiny machines will determine success on the battlefield. The author writes:

This is a game of combat in the realm of miniaturized warfare, which re-creates the struggle between hunter-killer groups of tiny fighting vehicles called MGVs. In Invisible Enemy, the heavy fighting is either over, or its a hundred feet away. On this battlefield, there are only a few units left and they must hunt each other down and clear the field; targets must be secured, gauntlets run or a final swipe at launching a surgical strike. No matter what the original mission was, things have changed and now the remaining units must finish it. Despite their microscopic size, it is the MGVs that always end up doing the heavy lifting.