According to the project, the Phase I milestone is to:
Demonstrate a ChemBot, approximately the size (but not necessarily the form-factor) of a regulation softball (i.e., 30 cm circumference; 10 cm diameter; 500 cm3 volume), that can:This means that your softball would be able to roll under your door, reconstitute itself, then perform some kind of function using its embedded payload. Picture the flying razor/drill balls from Phantasm, and you could see how gnarly the application could manifest itself. The bad guy from Terminator 2 is also an acceptable analogy.
a) travel a distance of 5 meters at a speed of 0.25 meters/minute;
b) achieve a 10-fold reduction in its largest dimension;
and c) traverse through a 1 cm opening of arbitrary geometry and reconstitute its original size and shape, in 15 seconds.
Past projects of DARPA have involved achieving Metabolic Dominance (providing soldiers superior physiological qualities), portable medical triage devices designed for warfare, and mutant ill-tempered sharks with frickin' lasers attached to their heads.
For more information, I recommend you read Philip K. Dick's short story, "The Little Black Box".