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.
The Intel Software Development Emulator is a functional emulator for new and upcoming instruction set extensions. The emulator is based on the Pin dynamic binary instrumentation system (and XED). It emulates the new instructions in the SSE4, AES, PCLMULQDQ, and RTM, BMI1, and BMI2 Intel AVX, AVX2, and AVX512 instruction set extensions. This allows developers to gain familiarity with Intel's upcoming instruction set extensions.
QEMU is a fast processor emulator. Using dynamic translation it achieves a reasonable speed while being easy to port to new host CPUs. In its user mode emulation mode, it can launch Linux processes compiled for one CPU on another CPU. Linux system calls are converted because of endianness and 32/64 bit mismatches. In its full system emulation mode, it emulates a full system, including a processor and various peripherials.
Mini vMac emulates a Macintosh Plus, one of the earliest of the Macintosh computers. It can run old Macintosh software that otherwise couldn't be used on recent machines. Mini vMac requires a ROM image file to run, and so can be legally used only by those who own a Macintosh Plus.