I was reading a comparison between Q2A and OSQA here:
http://meta.draw3cards.com/questions/365/should-we-consider-question2answer-as-an-osqa-replacement
and here:
http://meta.osqa.net/questions/6654/has-anyone-compared-osqa-to-question2answer
and they gave a few reasons against choosing Q2A, one of which was not being able to close questions. I couldn't quite understand the need to close questions at the time, but I see Stack Exchange closes questions, and gives a reason why it was closed and who closed it - that seems like a good idea, so, here is a question-closing plugin:
https://github.com/NoahY/q2a-close
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Features
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- allows closing questions, which removes ability to answer, comment or vote on them.
- admin and mods can close questions by default
- optionally allow closing own questions
- adds notice below closed questions with linked name of closer and reason
- adds text to closed question titles
- all text fully customizable
Screenshot:

You can also include links to other questions in the reason:

Any thoughts?