Algodoo

You might think now "Lol, there were already engines which use Negative Springs, what is so special about this one?"
So, here are some answers. If they are more pros or cons you decide yourself:

- It is in the wheels, so it even suits into small machines

- As far as I can see is it currently one of the fastest

- It only needs a very few parts to be built (interesting for people who only have the demo of Algodoo, like me and for those who have not that fast PCs again like me)

- It is quite heavy

- It works with absolutely 0 collision layers

To start it press left or right arrow till the orange box has a velocity of about 3.7m/s, then release it and wait. You can try to brake it with down arrow, but that's actually a quite dumb idea.
Please rate and comment. And do not rate it down, just because I chose the classic box-on-wheels-design!