Good Free Online Games?

I was wondering if there is any good free online games that anyone knew of? I just need to play these when I get bored of my other games. A good offline game would work also just prefer online.

Starknights is a classic online space rts/action game. There are dozens of browser-based space games out there but Starknights uses stand-alone client and is much better than any of those. You can find it at www.starknights.com
It was released almost ten years ago but it is still very addictive. You can produce different types of starships and create fleets, produce and put different components on your ships, colonise planets and build different buildings on them, use a market system. The strategic element of the game resembles Master of Orion and the action side of the game reminds of Star Control (two old classic space games from the 1990s).