They seemed to explode on to the scene around ten years ago as the future of on-line collaboration and communication, and quickly became a mainstay of tech companies/projects as their knowledge base and documentation. I have worked on several large tech projects as a consultant over the last decade, and almost all of them treated getting a wiki setup only second to basic infrastructure and version control.
Thing is though, they kinda suck.
A few years ago I was working as a consultant on a large, internationally based project, and found myself thinking about the fragmentation, and frankly the madness, of the variety of communication and collaborative tools that were being used. We had messaging apps, email, about three different ticketing systems and a wiki, which lead me to think more about wikis.
They became popular because they suggested collaborative writing and editing of documents, and I guess a lot of managers grabbed hold of it as a way to get developers passionate about writing documentation and capturing the teams knowledge. But at the end of the day, writing documentation is still just as dull as ever - developers still won’t enjoy it, even if it is in a wiki rather than a Word doc. And assuming you are able to get them to write the docs in the first place, there is no user engagement or incentive to keep it up to date. The second someone actually finds something on the wiki isn't correct/working, they will just go ask someone.
Personally, I like the Q’n’A site model a la StackOverflow.com. It doesn't fit across the board (still a place for more formal documentation etc), but it seems like a much better model for capturing company/project knowledge.
Wikis don’t seem to offer much over normal documentation approaches (and seem to offer less than something like Google Docs, which would seem to have superior collaborative tooling).
Forums would offer a more conversation lead approach, which I think would increase user engagement, but it can be hard to find answers amongst a sequential conversation thread.
A Q’n’A site seems to offer the best, with a more conversation based approach for a better, more engaging user experience, but with crowd sourced, peer-verified answers, making it easy to find the answer you are looking for. Throw in the gamification approach StackOverflow uses for good measure and I suspect you may see your knowledge capital growing pretty quick.
It surprises me that there isn't an established, open-source Q’n’A product.