Algodoo

This contraption is a binary counter/adder. Each of the levers starts off pointed to the left, which reads as zero 64s, zero 32s, zero, 16s, and so forth.
If you drop a ball into the top, the machine will count the balls and represent the number in binary. You can also add numbers by inserting balls in the left.
So suppose, for example, you wanted to add 10 + 6 in binary. You would begin by entering ten: + 8, +2. Then, enter six: +4, +2. The sum, 16, shows on the right. (And, just for fun, it looks like a boat.)