CWG_ODE is a FORTRAN77 library which includes three solvers for systems of ordinary differential equations, written by C William Gear.
CWG_ODE is available in a FORTRAN77 version.
DFIELD8, a MATLAB program which interactively displays the direction field of a differential equation, by John Polking.
DRIV, a FORTRAN77 library which solves real or complex systems of ordinary differential equations;
NMS, a FORTRAN90 library which includes the DDRIV< package of ODE solvers.
ODE, a FORTRAN77 library which solves a system of ordinary differential equations, by Shampine and Gordon.
ODEPACK, a FORTRAN77 library which contains nine ODE solvers, including LSODE, LSODES, LSODA, LSODAR, LSODPK, LSODKR, LSODI, LSOIBT, and LSODIS, by Alan Hindmarsh.
PPLANE8, a MATLAB program which interactively displays the phase plane of a differential equation, by John Polking.
RK4, a FORTRAN77 library which applies the fourth order Runge-Kutta algorithm to estimate the solution of an ordinary differential equation at the next time step.
RKF45, a FORTRAN77 library which implements the Runge-Kutta-Fehlberg ODE solver.
TEST_ODE, a FORTRAN90 library which contains routines which define some test problems for ODE solvers.
You can go up one level to the FORTRAN77 source codes.