Integrate
Integrate is a package to aid in solving differential equations, currently slightly limited in scope.

It was developed specifically to solve geodesic equations in 5 dimensions, but is completely general in application (as long as the system is of the form {d^n(x1)/dt^n = f(x1,\dot{x1},...,xn,...,t), ...}). Advantages over other Mathematics packages include customizability of the integrator and of stopping conditions, and the natural introspective nature of lisp. It is available from (the older version of) cCLan and the code is placed in the public domain.

There is also a Debian package.