CPUlator has played an instrumental role in my ARM-based Assembly explorations. One can simulate a full system, including not just the processor, but also the peripherals and the system-on-a-chip interconnects, mimicking a real system's behavior. I really appreciate the ability to inspect the memory as well as the individual registers as you are running a program.

The possibility to show real-time visual feedback and debugging capabilities provides an excellent avenue for people to understand the nuances of computer architecture. Through CPUlator, I have been able to guide learners through the use of ARMv7 assembly instructions and their usage who might not have access to ARM hardware themselves. I can't recommend this tool enough.