MAME: Multiple Arcade Machine Emulator.
It's a program you can download for free and it lets you play classic arcade games. Each game is called a "rom", so after downloading mame (a VERY small program) you have to add roms.
You can get mame (version 32) here:
http://www.whiper.com/mame/
It may appear confusing at first, but it's really easy to use mame. To give you an example: 1) Download and install mame32, 2) Here you can find roms (games) by letter:
http://www.rom-world.com/dl.php?name=MAME&letter=F From here, download Final Fight (World). The name of the file is ffight, so go to the "roms" directory in your mame folder, create a folder named "ffight" and extract the file there. Then you can run the game by executing mame32.exe and choosing Final Fight (World) from the list. Oh and in order for mame to know which roms you have installed, you have to go to the "File" menu and press "Audit all games".
Here's a mame guide:
http://www.mame.net/mamefaq.html
And here's a screenshot of Final Fight; I'm sure many of you know it:

If irony were made of strawberries, we'd all be drinking a lot of smoothies right now.