http://www.tokamakphysics.com
It's free to download, but I think the EULA may trip us up a little.
The LICENSEE may not redistribute the SOFTWARE, except as part of a compiled software program that is not itself a physics library.
OK, this says that it's ok to redistribute it provided it's part of your compiled executable. Fair enough, but we can't do that in DBP. We'd need someone to compile it as a DLL for us to use, therefore making a compiled software program which is itself a physics library; Does that make mean we're breaking the EULA?
I opened the case to my PC today and thought, my exhaust fan sucks.