stackoverflow clones

After the success of stackoverflow, many applications with similar concepts have emerged.
while some of the chinese sites have even used the same design, some of the web applications are geniune attempts to add value.
O'Reilly with its vast knowledge base of everything related computers is trying to take advantage of it with O'Reilly Answers concept.

What other sites do you see as a stackoverflow competitor?

Update here is once stackoverflow wanna be in Turkish
http://www.sonsuzdongu.net/