title: Open source physics engines
body: <p>I have been using <a href="http://www.ode.org/" rel="noreferrer">the Open Dynamics Engine (ODE)</a> for the last few weeks with great success. It has a very simple API and its simulations at least <em>look</em> realistic. (I sometimes wonder about my collision joint parameters, but whatever.)</p>
  
  <p>My only complaint is that it is sometimes a dog. If I naively simulate 1000s of interacting bodies, then my performance starts to dive.</p>
  
  <p>I know I can spend time with their spatial grids to reduce the load of the collision system, but before I go through the effort of tuning my code to work with ODE, I wonder if there are <strong>any other Open Source/Free physics engines worth looking at</strong>. This will be for a commercial app, so I am looking for something more solid and more battle tested than some college student's weekend project.</p>