Favored Freeware: MacMAME

MacMAME is part of the MAME project, a non-profit organization dedicated to preserving the history of arcade videogames via emulation. MacMAME achieves this by running the original program code found in the arcade games. As such, it is much more than a reproduction, it is essentially that same game running via an emulated layer inside your Macintosh.

Pros: Easy to setup, nearly flawless emulation, good graphics filters.

Cons: Some ROMs are broken or function poorly. It is illegal to play these games (ROMs) unless you own them, or you only play them for a period of up to 24 hours. After which, you must delete the game. If you do not own the game and you have played it for more than twenty-four hours, then you are in violation of federal law and you will be prosecuted.

Note: Do not ask me for ROMs.