http://www.ogame.org/
Yes, I play that game every now and then. It doesn't make you feel like a downs baby by playing it like Runescape does, and still runs in a browser. Works in Linux or Windows, like Mac too. I played it off and on for a few years for free, never thought their pay plan was worth it because it's a simple browser game but I had so much fun derived from it over a long period of time I'm putting a link up to anyone who would want to join up with me in-game sometime.
Maybe we can get a GOG cabal going in a few universes. I am on universe 42, 43, and Fornax universe. Those are ones with the new interface, same as old ones but looks much better. I am TB87670 in the game, contact me if you want and hope to see some of you around.
EDIT: Forgot to mention Universe 42 goes double speed as Fornax and 43, and I always play by opening 3 tabs in firefox and having each universe in one of the tabs. That way I triple what I do before waiting for stuff to get done. This is a great game to play in the office because you can exit anytime and come back whenever.