Bochs is a highly portable open source IA-32 (x86) PC emulator
written in C++, that runs on most popular platforms.  It includes
emulation of the Intel x86 CPU, common I/O devices, and a custom
BIOS.  Currently, Bochs can be compiled to emulate a 386, 486,
Pentium, Pentium Pro or x86-64 CPU, including optional MMX, 
SSE/SSE2/SSE3 and 3DNow! instructions.  Bochs is capable of running
most Operating Systems inside the emulation including Linux, DOS,
Windows 95/98 and Windows NT/2000/XP.

Bochs has some dependencies for the display options: SDL, libsvga, 
wxWidgets (any of three versions [GTK, Motif, X11] run very well), 
but they are not necessary at all (because autodetection runs very 
well). The only one really needed is Xlib.