I would like some super simple computational code for solving magnetohydrodynamics problems. High accuracy nor performance is not my concern. I wan't it just to visually explore qualitative behavior of plasma. Important for me is:Generality - it should not be specialised on any particular subproblemof MHD Easy to get it work - does not require any libraries difficult to instal. Input is strightforward and well documented by some examplesEasy to read and modify - you can read the code and learn about MHD solution from it. You can use this code as starting point for your own MHD code development Something as simple as this Navier stokes solver would be bestbest would be something in python-numpy or java, but C++ or Fortran is not a big  problem for me.Up to now I found:some libraries ( MHD-Hermes and python-mhd ) which are in python, but doesn't seem to have any documantation or examples how to use it.and this A Free, Fast, Simple and Efficient TVD MHD Code which is in frotran but has just 400 linesI was thinking about writing something by myself but I want to be sure there is nothing similar already avaible. I think it could be quite easy, just take the Navier-Stokes solver from the link above and introduce electric and magnetic potential by FFT poisson solver ( or Particle Mesh Ewald ).  
simple MHD simulation code for (self) education and play with
fluid dynamics;education;electromagnetism
Have a look on these three:Piernik MHD it is a code which evolved from the Pen & Trac MHD you mentioned in your question. Now its quite mature and the development is still active. Written in modern Fortran 95/2003.Godunov MHD an MHD code designed especially for simulating the reconnection events, but can be easily modified and applied to other problems. It can be parallelized from single multicore machine (OpenMP) up to clusters with many nodes (MPI). Written in Fortran 90/95.python-mhd a small and simple MHD code, easy to play with it. Written in Python and C.