I misunderstood and thought you just wanted a file uploading site to check for viruses. Now there are pictures attached, please take a look. I don't think I can do more than this without going open source, and I want to wait with that until I am finished with my ideas.
The library is not complete and clicking in the tree will deactivate it, just click on the top item or reopen to reactivate.
Biggest problem: When the simulation is stopped octave is stopped with a destroy command from java. This often causes Octave to crash which really is not a problem since GoSim doesn't crash but Xubuntu (and probably other Linuxes) gives this dialogue that octave crashed and do you want let the developers know.....bla bla. For endusers this is not very nice. I have no other way to stop Octave running a script. If you know please tell.
Adding blocks is very simple, I have many blocks that can be used as templates. Many people like working with block diagrams and Octave doesn't have it so I think it will add good functionality for you. Anyway, let me know.
pid.gsm requires the control toolbox to be installed, one of the blocks (GoSimControl) uses commands from it.