Just want to clarify. Do you want free games which you can download online but play on your PC or exactly as you have asked which I interpreted to mean, you want free games which you can play online. It would also help if you stated what genre you like eg sims, action/drama, racing, board games, etc.
I see. Nothing free comes readily to mind at this very moment but don't despair stick around and I'll see what I can come up with. In the mean time feel free to browse around in this forum http://forums.afterdawn.com/forum_view.cfm/168 the any other forums and maybe you might even find something you're interested in.
