Is there any q&a site where answers can be edited collective, as in a wiki, in order to create the best possible reply?
Just like wikipedia, but instead of articles it's questions.
Potentially allow for several answers, but the main goal would be to create the best answer using the same criteria we use for wiki articles.
Stackoverflow and the associated sites are more or less like that. It sometimes has problems with overzealous users marking tangentially related questions as duplicates but overall it seems to work.
Downvoting costs karma and it's encouraged to give reasons for a downvote. If an answer is outdated a newer answer often quickly rises to the top and often enough the original answerer will promote the better answer. And you can also edit other people's answers and you can see an edit history.
But it only works if there are enough knowledgeable people participating. It's especially bad with new questions because either the question is low quality or the first answer which gets accepted by the questioner right away is bullshit.
The other thing that makes stack overflow good is that it's a very specific problem, with a this works/this doesn't result. Otherwise it seems to me like a collaborative Quora, which would be just as useful as regular Quora.
Stack overflow has a sibling site for nearly every category you can think of, honestly
World building is actually a lot of fun to peruse.
Are you looking for WikiHow?
Dedicated forum sites. I've received good tips from stackoverflow, ltt forum, arch Linux forums and wiki.
Stack Overflow does this
There is a "extra step" to q&a sites where you generalize the tangental questions and answers into a wikihow blog post. The sites themselves aren't able to do it gracefully, but there are several one off blog posts that are gold mines from stack overflow.