Stackoverflow had been down for about an hours, now it's back but still not functioning. I was bored, then I noticed the address, you can see at the bottom of the screenshot:
http://stackoverflow.com/error?aspxerrorpath=/

So? Windows? or via Mono on Unix-like system? (I have no idea if Mono can do that or not)

Well, actually it doesn't matter.

Hurry come back, Stackoverflow! Stop being overflow! :D

(Right after posted, it now says "Stack Overflow is currently offline for maintenance")