Wine is an implementation of the Windows API on top of X and Unix. It does not require Microsoft Windows, but can use native Windows DLLs if they are available. It provides both a development toolkit for porting Windows source code to Unix as well as a program loader, allowing many unmodified Windows programs to run on x86-based Unixes.
Bochs is a powerful x86/amd64 hardware emulation and debugger software. Besides the CPU and instruct set extensions, it simulates common PC/AT hardware, an ISA and PCI system bus, memory, disks, video hardware, ethernet, and enough of a compatible BIOS to run DOS/Winows, Linux/BSD, Minix and other operating systems. It doesn't provide virtualization, thus runs extremely slow, but is safe to run for the host operating system.