No, I'm not talking about pirating or anything like that. Instead, the good people at Archive.org have just opened up a new project that they're calling the Console Living Room. When you head on over in that direction, you'll find no fewer than 994 video games for you to enjoy. These are all for free, as their intellectual property protections have expired, and you can play them from directly within your browser, including some controller support. You can also play them with a keyboard if that's easier.
Naturally, since we're talking about classic consoles and expiring copyrights, the games are going to be on the older end of the spectrum. They currently carry titles from the Atari 2600, Atari 7800 ProSystem, ColecoVision, Magnavox Odyssey and Astrocade. The browser-based games use the JSMESS emulator system, but there is currently no sound. That's going to be addressed soon.
You can find the Console Living Room on Archive.org. Now, if you'll excuse me, I have some missiles to command.