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Which Content Management System (CMS) should I use?

I am looking to start a new forum, with a traditional forum layout (like webhostingtalk, for example).

In this space, I know phpBB and SMF are strong contenders. I do not know for sure the names of other great forum software that might exist...

My most important need is that it should be easy to modify the display area, at the least, without having to dig too much into the core. Drupal excels in this area with its templating system, but the forum module doesn't look like the forum interface most people are used to...

It would be a great plus if the software has alternative Captchas like question based or invisible Captcha. If it doesn't, I would like to be able to code it in without much trouble (that is, the software exposes a good API)