Sites

N-Body/Particle Simulation Methods (Popularity: )
http://www.amara.com/papers/nbody.html
An extensive online tutorial with examples and code references.

ORSA - Orbit Reconstruction, Simulation and Analysis (Popularity: )
http://orsa.sourceforge.net
ORSA is a C++ framework for the development of algorithms and programs oriented to the simulation and analysis of the orbital evolution of bodies in space.

Aarseth's N-body software (Popularity: )
http://www.ast.cam.ac.uk/~sverre/
[open source - multiplatform] Direct N-body algorithms.

Gravit (Popularity: )
http://gravit.slowchop.com
Gravit is a gravity simulator which runs under Linux, Windows and Mac OS X. It's released under the GNU General Public License which makes it free. It uses Newtonian physics ...

Barnes & Hut Treecode Algorithm (Popularity: )
http://www.ifa.hawaii.edu/~barnes/software.html
[open source - multiplatform] A guide to a tree code algorithm implementation, used for astronomical N-body simulations.

NEMO (Popularity: )
http://bima.astro.umd.edu/nemo/
[open source - Unix] An extendible stellar dynamics toolbox; has various programs to create, integrate, analyze and visualize N-body and SPH-like systems. In addition there are various tools to operate ...