Bochs

"Bochs (pronounced "box") is a portable IA-32 and x86-64 IBM PC compatible emulator and debugger mostly written in C++ and distributed as free software under the GNU Lesser General Public License. It supports emulation of the processor(s) (including protected mode), memory, disks, display, Ethernet, BIOS and common hardware peripherals of PCs.

Many guest operating systems can be run using the emulator including DOS, several versions of Microsoft Windows, BSDs, Linux, Xenix and Rhapsody (precursor of Mac OS X). Bochs runs on many host operating systems, including Android, iOS, Linux, Mac OS X, PlayStation 2, Windows, Windows Mobile.

Bochs is mostly used for operating system development (when an emulated operating system crashes, it does not crash the host operating system, so the emulated OS can be debugged) and to run other guest operating systems inside already running host operating systems. It can also be used to run older software – such as PC games – which will not run on non-compatible, or too fast computers.

Bochs emulates the hardware needed by PC operating systems, including hard drives, CD drives, and floppy drives. It doesn't utilize any host CPU virtualization features, therefore is slower than most virtualization, rather than emulation, software. It provides additional security by completely isolating the guest OS from the hardware. Bochs also has extensive debugging features. It is widely used for OS development, as it saves the need for constant system restarts (to test code)."

https://en.wikipedia.org/wiki/Bochs

http://bochs.sourceforge.net/