From the RetroArch homepage:

RetroArch is a multi-system emulator for Linux, Windows, Mac OS X and *BSD. It is formerly known as SSNES.

Its design and background is quite different than most other emulators as RetroArch does not implement an emulation core itself. RetroArch talks to libretro, a generic emulator core API. This means that RetroArch is core agnostic, and it does not care which emulator core is running.

Currently there are libretro implementations for systems such as SNES, NES, GBA, GB/GBC, Genesis, and even arcade games (Final Burn Alpha).

Downloads Windows Mac OS X Linux Android
Windows builds and release notes ✓* Source code
Mac OS X builds