EdSim51
The 8051 Simulator for Students and Educators
...The student can write 8051 assembly code, step through the code and observe the effects each line has on the internal memory and the external peripherals. Code written in C can also be imported into the simulator.
Find out more, including the installation instructions and the user's guide at edsim51.com.
You're obviously into technology. How about alien technology?
James Rogers doesn't just write software. He is also a novelist. Each download of EdSim51 includes a free chapter of Flight of the Eternal Emperor: jameswrogers.com