Algodoo

Can take up to 11,000 Nm braking force on the central hinge before stalling. This number will vary, of course, depending on what you attach it to (I'm not sure how hinging to the background works...). But it's pretty powerful in any case.

It also doesn't have any external torque (no negative-length engines do). That means you can use one and it won't make whatever you put it on do flips.

I would not recommend connecting any drivetrain to it directly. Instead, add 4 more circles near the middle, hinge them to the motor, and then use 4 identical circles hinged to your drivetrain of choice, and "Glue Together" each circle to its counterpart on the other large circle. This was Bronie1234's idea, I think, but it works very well for this type of engine because it puts a buffer between it and the drivetrain�it really doesn't like being jostled, to the point that just touching another circle to it makes it erratic.