John Chambers Mercury package for amuse.

Mercury is a symplectic planetary integrator
available at http://www.arm.ac.uk/~jec/home.html

references:

"A Symplectic Integration Scheme that Allows Close Encounters between 
Massive Bodies."
J.E.Chambers (1999) IAU Colloquium 172, `The Impact of Modern Dynamics in 
Astronomy, 449-450.

"A Hybrid Symplectic Integrator that Permits Close Encounters between 
Massive Bodies."
J.E.Chambers (1999) Monthly Notices of Royal Astron. Soc., 304, 793-799.

"Mercury - A New Software Package for Orbital Integrations."
J.E.Chambers and F.Migliorini (1997) Bull. American Astron. Soc., 29, 
1024. 
