Algodoo

4 bit Arithmetic-logic unit capable of doing:
-addition
-AND
-OR
-XOR
on two inputs.
It's my own design, not based on popular flip-flops. The advantage is that the output is in the same format as input (row of marbles-bits). Operation selection is controlled by 3-bit input, plus 4th bit to start.

It took me quite a lot of planning, so please comment and give suggestions.
Negative number handling is underway