The Internet Archive has opened access to a library containing over 900 arcade games that are playable in-browser, although some may not work quite well just yet.
Dubbed the "Internet Arcade", the library provides research, comparison and entertainment to users.
Be warned though that some games won't work as nicely as others. They are emulated in JSMAME, part of the JSMESS software package, and aren't completely bug-free by any means. Additionally, some aren't really suited to a keyboard / mouse input.
Still, you can have fun shutgunning through them at: archive.org.












