There's a new gaming website called Instant Action that lets you play multiplayer 3D games in real-time in your web browser. It uses a browser add-on but I think it's cross-platform because it's all in the browser.
Anyway, it's in a pseudo closed beta right now. I was accepted into the beta and anyone I invite will also be accepted. There are only four games to choose from for now but at least two of them are kind of fun, depending on your play style. The reason why I only say two is because I haven't yet tried the other two in a multiplayer setting.
If you'd like to check it out and play with me (and other DC members) express your desire here and/or send me a PM with an e-mail address I can send the invitation to.
If anyone's heard of Marble Blast Ultra or Think Tanks (made by GarageGames), those are the two games I said are fun for sure.
Please note that this offer is for current DC Members. If you found this post from a search somewhere and came here looking for free goodies, then this may not be the place for that.