General Runge-Kutta Solver for Planar Dynamical Systems
This is a general ODE solver that uses the O(Δt5)O(Δt5)-accurate Runge Kutta scheme with a fixed time step. I have also added buttons corresponding to the equations of a Simple Harmonic Oscillator, the FitzHugh-Nagumo equations, the Two-Pool model of cellular calcium dynamics and the Lotka-Volterra Predator-Prey Model. There are things that should be improved in terms of how the scheme is implemented, but it should let you solve any autonomous 2-D dynamical system that you like.
I have recently stumbled upon Darryl Nester's excellent ODE Tool which essentially has all of the features of the above implementation in addition to others such as a visualization of direction fields and integral curves, as well as being able to follow a solution trajectory in both phase space and in time. Here is a link to that solver with the Two-Pool model entered.