There are other free libraries out there. This Solver
could support them all (have an optionbox to choose the
internal solver).. or we can split off seperate solver
nodes. Depends on how similar the API's are I guess.
Not a high priority, something to think about.
Here are some other libs out there:
http://physicsengine.com/index.html
http://www.tokamakphysics.com/
http://www.continuousphysics.com/Bullet/