Blocksim is a very experimental, untested, super tiny graphical tool for numerical simulation. At this point, it is not meant to be used for anything other than experimenting and having fun.
I have written a small blog post about modeling and simulating a simple mass-spring-damper system, which is available here. If you have never used something like MATLAB/Simulink or Scilab/Scicos, it might be informative.
As said above, it is a very young weekend project, so please report the bugs you find. I would also love to hear about what you're doing with it. Thanks!
Contact: rbaron (a_t) rbaron.net