Mac: OpenEmu is an all-in-one video game emulator where you can emulate your games, create collections and set up controllers for classic controls.
OpenEmu is powered by open source emulators, which means it can emulate Nintendo, Super Nintendo, Megadrive, Turbografx-16, and plenty more. It's also incredibly easy to use. You can set up controllers with different layout schemes for each console you're emulating, organise your games by console or into different libraries, and of course, play games.
OpenEmu scans your hard drive for games, supports lots of popular controllers out of the box, and automatically pulls the box art for you. Basically, it's the last emulator you'll need for your Mac.