Wine

Wine lets you run Windows software on other operating systems. With Wine, you can install and run these applications just like you would in Windows.

Wine is still under active development. Not every program works yet, however there are already several million people using Wine to run their software.

Frontends:

Popular forks:

System requirements: 

x86 compatible CPU

Comments

Wine
Is
Not a
Emulator

It does not emulate Hardware but you could say it emulates direct3d for opengl.