I once reverse-engineered the complete instruction set of the CPU in a pocket calculator with a built-in BASIC interpreter. That was fun. My disassembler and assembler BASIC programs are still functional today.
It's a Sharp PC-E500S. The BASIC has PEEK, POKE, and CALL (for running assembly) commands, which is all you need for a hacking orgy. I'm not sure you could even still get hold of that hardware today.
