We support operating systems that not even Microsoft and Apple themselves support anymore, such as macOS X on PowerPC Macs, and RetroArch being available on Windows OSes as far back as Windows 95. For instance, an emulator will let you use an arcade machine that no longer exist or use a game console that can no longer be. In other words, it allows you to use software meant for another system that you may not have access to by running a program on your system.
RetroArch can run on the usual platforms like Windows, Mac OS X and Linux, but it stands alone in that it can support far more platforms beyond just that. Emulation is the process of simulating the hardware of one computer (particularly the processor) via software on a different one.
