http://www.minecraft.net/ it doesn't look like it'd be fun at all but it IS haha. It's an indie game too.
Yes, I got the paid version which is quite an amusing time waster now and then, but I mostly play the classic version. I just run my own private server and mess about on that
I love the collaboration in minecraft online, it's actually a really addictive game and takes me back because of its 8bit graphics. I have two servers right now, and I play with some friends every now and then