Ooh, my favourite cross-platform multi-system emulation behemoth, RetroArch, just updated to v1.7.3 to include a desktop-style GUI for Windows and Linux, with OSX to come soon.
It's not much of a GUI right now, but now that it's in place, we should start seeing all kinds of interesting developments that'll make it easier to set up and use the platform, because let's face it... UI designed for gamepads or touchscreens can be great for some tasks but lousy for others.