[ctas]

There were a few attempts at this in the past, even before StackOverflow existed and they always failed. I remember listening to a podcast which dissected the success story of StackOverflow and how it improved on its predecessors. One point I remember taking away was that all predecessors that used money to attract answers were less effective than the counterparts that solely relied on non-monetary rewards such as upvotes, karma, a simple "thank you" and other kinds of social approval.

Sorry for not being able to back this with the original sources.