I don't know. There are cycle-accurate FPGA implementations of the old MPUs, but I wonder how common a software simulator is. Non-cycle-and-system-incorrect software simulation is probably okay for most applications. I commented on another thread about the impracticability of substituting an NSC800 for an 8085 that used 8259 PIC, 8257 DMA and 8202 DRAM controller--and that's hardware for hardware.
In the past, I've adapted an x80 software simulator to also simulate certain peripherals to replace commercial PLCs, so it's possible to get an acceptable result.
A few years ago, we had a forum member, I think his name was Valentin (don't recall his handle), who used a souped-up 8052 to simulate an 8088 PC, providing CGA graphics, sound and even supporting an ISA slot. It was pretty nearly time-accurate and was a real tour de force. Don't know what happened to his project, or him, for that matter.