If by 'online' you mean 'multiplayer' then check out the BlitzPlay multiplayer code library at http://www.blitzcoder.com/blitzplay . There's a free version and a low cost commercial version.
If you mean a game that runs on a web server then, as Epicboy says, you need to be more specific. Try doing some searches for 'web server software', 'web server games', 'web server languages', 'online games', etc, on Google to research the subject further so you can ask better questions.
If you mean a game that runs on a web server then, as Epicboy says, you need to be more specific. Try doing some searches for 'web server software', 'web server games', 'web server languages', 'online games', etc, on Google to research the subject further so you can ask better questions.