'Old fossils' like me, had a computer like the commodore 64 in the eighties (I guess not a lot of people know this type of computer on this forum. They are too young!
). This computer had the 6510 CPU. Some 'freaks' had done a reverse engineering of this CPU and have done a simulator of the CPU ! (Not an emulator, a simulator !!!). I find their work amazing. You can find the result of the following website :
http://visual6502.org/. You can even simulate the CPU on your browser in this section ! :
http://visual6502.org/JSSim/index.html. To start the simulation, click on the 'start' button on the upper right.
An interesting video about the reverse engineering of the 6502 CPU :
http://www.youtube.com/watch?v=K5miMbqYB4E