Just came across this site: http://www.puzzleoverflow.com
It looks exactly the same as a Stack Exchange site. It doesn't seem to have any connection with SE, though, and it's not mentioned on Stack Exchange or anything.
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It is a StackExchange site. In addition to checking the metadata, you can also visit it at http://puzzleoverflow.stackexchange.com/
It was a Stack Exchange 1.0 puzzle site. It was a lot of fun and I think it'd have a place as part of a larger Stack Exchange built around Interviewing. But There isn't one of those yet.