There are a couple of shells available for the TI-83 except some of them are hardly ever used now. The two main TI-83 Shells are AShell83 and Ion. Ion is actually the newer two, but it has really caught on because it's also used in the TI-83 Plus. Actually, AShell83 has been around since the end of 1997, but it's still used a whole lot still. There are two other types of shells. The first one is SOS, which I don't think is used that much, though because not that many programs are made for it. The last shell is TI-Explorer. I have never used TI-Explorer before, but it can run AShell, SOS, and Ion programs. You see the other shells can't run programs designed for other shells, but TI-Explorer can run all three types of programs. Like I said, I've never used it, but it seems to be the best since it can run all types of assembly programs. There are still however some more shells, but I haven't even heard of them before or used them. To check them out and all the other shells I told you about, click here.