Bochs is a highly portable open source IA-32 (x86) emulator written in
C++, that runs on most popular platforms. It include emulation of the 
Intel x86 CPU, common I/O devices, and a custom BIOS. Bochs can be 
compiled to emulate 386, 486, Pentium/Pentium II/Pentium 4 or x86-64 
including optional MMX, SSEx and 3DNow! instructions.

wxPython is an optional dependency.
